[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7. Operating on sorted files

These commands work with (or produce) sorted files.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.1 sort: Sort text files

sort sorts, merges, or compares all the lines from the given files, or standard input if none are given or for a file of `-'. By default, sort writes the results to standard output. Synopsis:

 
sort [option]… [file]…

sort has three modes of operation: sort (the default), merge, and check for sortedness. The following options change the operation mode:

`-c'
`--check'
`--check=diagnose-first'

Check whether the given file is already sorted: if it is not all sorted, print a diagnostic containing the first out-of-order line and exit with a status of 1. Otherwise, exit successfully. At most one input file can be given.

`-C'
`--check=quiet'
`--check=silent'

Exit successfully if the given file is already sorted, and exit with status 1 otherwise. At most one input file can be given. This is like `-c', except it does not print a diagnostic.

`-m'
`--merge'

Merge the given files by sorting them as a group. Each input file must always be individually sorted. It always works to sort instead of merge; merging is provided because it is faster, in the case where it works.

A pair of lines is compared as follows: sort compares each pair of fields, in the order specified on the command line, according to the associated ordering options, until a difference is found or no fields are left. If no key fields are specified, sort uses a default key of the entire line. Finally, as a last resort when all keys compare equal, sort compares entire lines as if no ordering options other than `--reverse' (`-r') were specified. The `--stable' (`-s') option disables this last-resort comparison so that lines in which all fields compare equal are left in their original relative order. The `--unique' (`-u') option also disables the last-resort comparison.

Unless otherwise specified, all comparisons use the character collating sequence specified by the LC_COLLATE locale.(2)

GNU sort (as specified for all GNU utilities) has no limit on input line length or restrictions on bytes allowed within lines. In addition, if the final byte of an input file is not a newline, GNU sort silently supplies one. A line's trailing newline is not part of the line for comparison purposes.

Exit status:

 
0 if no error occurred
1 if invoked with `-c' or `-C' and the input is not sorted
2 if an error occurred

If the environment variable TMPDIR is set, sort uses its value as the directory for temporary files instead of `/tmp'. The `--temporary-directory' (`-T') option in turn overrides the environment variable.

The following options affect the ordering of output lines. They may be specified globally or as part of a specific key field. If no key fields are specified, global options apply to comparison of entire lines; otherwise the global options are inherited by key fields that do not specify any special options of their own. In pre-POSIX versions of sort, global options affect only later key fields, so portable shell scripts should specify global options first.

`-b'
`--ignore-leading-blanks'

Ignore leading blanks when finding sort keys in each line. By default a blank is a space or a tab, but the LC_CTYPE locale can change this. Note blanks may be ignored by your locale's collating rules, but without this option they will be significant for character positions specified in keys with the `-k' option.

`-d'
`--dictionary-order'

Sort in phone directory order: ignore all characters except letters, digits and blanks when sorting. By default letters and digits are those of ASCII and a blank is a space or a tab, but the LC_CTYPE locale can change this.

`-f'
`--ignore-case'

Fold lowercase characters into the equivalent uppercase characters when comparing so that, for example, `b' and `B' sort as equal. The LC_CTYPE locale determines character types. When used with `--unique' those lower case equivalent lines are thrown away. (There is currently no way to throw away the upper case equivalent instead. (Any `--reverse' given would only affect the final result, after the throwing away.))

`-g'
`--general-numeric-sort'
`--sort=general-numeric'

Sort numerically, using the standard C function strtod to convert a prefix of each line to a double-precision floating point number. This allows floating point numbers to be specified in scientific notation, like 1.0e-34 and 10e100. The LC_NUMERIC locale determines the decimal-point character. Do not report overflow, underflow, or conversion errors. Use the following collating sequence:

Use this option only if there is no alternative; it is much slower than `--numeric-sort' (`-n') and it can lose information when converting to floating point.

`-h'
`--human-numeric-sort'
`--sort=human-numeric'

Sort numerically, as per the `--numeric-sort' option below, and in addition handle IEC or SI suffixes like MiB, MB etc (Block size). Note a mixture of IEC and SI suffixes is not supported and will be flagged as an error. Also the numbers must be abbreviated uniformly. I.E. values with different precisions like 6000K and 5M will be sorted incorrectly.

`-i'
`--ignore-nonprinting'

Ignore nonprinting characters. The LC_CTYPE locale determines character types. This option has no effect if the stronger `--dictionary-order' (`-d') option is also given.

`-M'
`--month-sort'
`--sort=month'

An initial string, consisting of any amount of blanks, followed by a month name abbreviation, is folded to UPPER case and compared in the order `JAN' < `FEB' < … < `DEC'. Invalid names compare low to valid names. The LC_TIME locale category determines the month spellings. By default a blank is a space or a tab, but the LC_CTYPE locale can change this.

`-n'
`--numeric-sort'
`--sort=numeric'

Sort numerically. The number begins each line and consists of optional blanks, an optional `-' sign, and zero or more digits possibly separated by thousands separators, optionally followed by a decimal-point character and zero or more digits. An empty number is treated as `0'. The LC_NUMERIC locale specifies the decimal-point character and thousands separator. By default a blank is a space or a tab, but the LC_CTYPE locale can change this.

Comparison is exact; there is no rounding error.

Neither a leading `+' nor exponential notation is recognized. To compare such strings numerically, use the `--general-numeric-sort' (`-g') option.

`-V'
`--version-sort'

Sort by version name and number. It behaves like a standard sort, except that each sequence of decimal digits is treated numerically as an index/version number. (See section Details about version sort.)

`-r'
`--reverse'

Reverse the result of comparison, so that lines with greater key values appear earlier in the output instead of later.

`-R'
`--random-sort'
`--sort=random'

Sort by hashing the input keys and then sorting the hash values. Choose the hash function at random, ensuring that it is free of collisions so that differing keys have differing hash values. This is like a random permutation of the inputs (see section shuf: Shuffling text), except that keys with the same value sort together.

If multiple random sort fields are specified, the same random hash function is used for all fields. To use different random hash functions for different fields, you can invoke sort more than once.

The choice of hash function is affected by the `--random-source' option.

Other options are:

`--compress-program=prog'

Compress any temporary files with the program prog.

With no arguments, prog must compress standard input to standard output, and when given the `-d' option it must decompress standard input to standard output.

Terminate with an error if prog exits with nonzero status.

White space and the backslash character should not appear in prog; they are reserved for future use.

`--files0-from=file'

Disallow processing files named on the command line, and instead process those named in file file; each name being terminated by a zero byte (ASCII NUL). This is useful when the list of file names is so long that it may exceed a command line length limitation. In such cases, running sort via xargs is undesirable because it splits the list into pieces and makes sort print sorted output for each sublist rather than for the entire list. One way to produce a list of ASCII NUL terminated file names is with GNU find, using its `-print0' predicate. If file is `-' then the ASCII NUL terminated file names are read from standard input.

`-k pos1[,pos2]'
`--key=pos1[,pos2]'

Specify a sort field that consists of the part of the line between pos1 and pos2 (or the end of the line, if pos2 is omitted), inclusive.

Each pos has the form `f[.c][opts]', where f is the number of the field to use, and c is the number of the first character from the beginning of the field. Fields and character positions are numbered starting with 1; a character position of zero in pos2 indicates the field's last character. If `.c' is omitted from pos1, it defaults to 1 (the beginning of the field); if omitted from pos2, it defaults to 0 (the end of the field). opts are ordering options, allowing individual keys to be sorted according to different rules; see below for details. Keys can span multiple fields.

Example: To sort on the second field, use `--key=2,2' (`-k 2,2'). See below for more notes on keys and more examples.

`--batch-size=nmerge'

Merge at most nmerge inputs at once.

When sort has to merge more than nmerge inputs, it merges them in groups of nmerge, saving the result in a temporary file, which is then used as an input in a subsequent merge.

A large value of nmerge may improve merge performance and decrease temporary storage utilization at the expense of increased memory usage and I/0. Conversely a small value of nmerge may reduce memory requirements and I/0 at the expense of temporary storage consumption and merge performance.

The value of nmerge must be at least 2. The default value is currently 16, but this is implementation-dependent and may change in the future.

The value of nmerge may be bounded by a resource limit for open file descriptors. The commands `ulimit -n' or `getconf OPEN_MAX' may display limits for your systems; these limits may be modified further if your program already has some files open, or if the operating system has other limits on the number of open files. If the value of nmerge exceeds the resource limit, sort silently uses a smaller value.

`-o output-file'
`--output=output-file'

Write output to output-file instead of standard output. Normally, sort reads all input before opening output-file, so you can safely sort a file in place by using commands like sort -o F F and cat F | sort -o F. However, sort with `--merge' (`-m') can open the output file before reading all input, so a command like cat F | sort -m -o F - G is not safe as sort might start writing `F' before cat is done reading it.

On newer systems, `-o' cannot appear after an input file if POSIXLY_CORRECT is set, e.g., `sort F -o F'. Portable scripts should specify `-o output-file' before any input files.

`--random-source=file'

Use file as a source of random data used to determine which random hash function to use with the `-R' option. See section Sources of random data.

`-s'
`--stable'

Make sort stable by disabling its last-resort comparison. This option has no effect if no fields or global ordering options other than `--reverse' (`-r') are specified.

`-S size'
`--buffer-size=size'

Use a main-memory sort buffer of the given size. By default, size is in units of 1024 bytes. Appending `%' causes size to be interpreted as a percentage of physical memory. Appending `K' multiplies size by 1024 (the default), `M' by 1,048,576, `G' by 1,073,741,824, and so on for `T', `P', `E', `Z', and `Y'. Appending `b' causes size to be interpreted as a byte count, with no multiplication.

This option can improve the performance of sort by causing it to start with a larger or smaller sort buffer than the default. However, this option affects only the initial buffer size. The buffer grows beyond size if sort encounters input lines larger than size.

`-t separator'
`--field-separator=separator'

Use character separator as the field separator when finding the sort keys in each line. By default, fields are separated by the empty string between a non-blank character and a blank character. By default a blank is a space or a tab, but the LC_CTYPE locale can change this.

That is, given the input line ` foo bar', sort breaks it into fields ` foo' and ` bar'. The field separator is not considered to be part of either the field preceding or the field following, so with `sort -t " "' the same input line has three fields: an empty field, `foo', and `bar'. However, fields that extend to the end of the line, as `-k 2', or fields consisting of a range, as `-k 2,3', retain the field separators present between the endpoints of the range.

To specify ASCII NUL as the field separator, use the two-character string `\0', e.g., `sort -t '\0''.

`-T tempdir'
`--temporary-directory=tempdir'

Use directory tempdir to store temporary files, overriding the TMPDIR environment variable. If this option is given more than once, temporary files are stored in all the directories given. If you have a large sort or merge that is I/O-bound, you can often improve performance by using this option to specify directories on different disks and controllers.

`-u'
`--unique'

Normally, output only the first of a sequence of lines that compare equal. For the `--check' (`-c' or `-C') option, check that no pair of consecutive lines compares equal.

This option also disables the default last-resort comparison.

The commands sort -u and sort | uniq are equivalent, but this equivalence does not extend to arbitrary sort options. For example, sort -n -u inspects only the value of the initial numeric string when checking for uniqueness, whereas sort -n | uniq inspects the entire line. See section uniq: Uniquify files.

`-z'
`--zero-terminated'

Delimit items with a zero byte rather than a newline (ASCII LF). I.E. treat input as items separated by ASCII NUL and terminate output items with ASCII NUL. This option can be useful in conjunction with `perl -0' or `find -print0' and `xargs -0' which do the same in order to reliably handle arbitrary file names (even those containing blanks or other special characters).

Historical (BSD and System V) implementations of sort have differed in their interpretation of some options, particularly `-b', `-f', and `-n'. GNU sort follows the POSIX behavior, which is usually (but not always!) like the System V behavior. According to POSIX, `-n' no longer implies `-b'. For consistency, `-M' has been changed in the same way. This may affect the meaning of character positions in field specifications in obscure cases. The only fix is to add an explicit `-b'.

A position in a sort field specified with `-k' may have any of the option letters `MbdfghinRrV' appended to it, in which case no global ordering options are inherited by that particular field. The `-b' option may be independently attached to either or both of the start and end positions of a field specification, and if it is inherited from the global options it will be attached to both. If input lines can contain leading or adjacent blanks and `-t' is not used, then `-k' is typically combined with `-b' or an option that implicitly ignores leading blanks (`MghnV') as otherwise the varying numbers of leading blanks in fields can cause confusing results.

If the start position in a sort field specifier falls after the end of the line or after the end field, the field is empty. If the `-b' option was specified, the `.c' part of a field specification is counted from the first nonblank character of the field.

On older systems, sort supports an obsolete origin-zero syntax `+pos1 [-pos2]' for specifying sort keys. This obsolete behavior can be enabled or disabled with the _POSIX2_VERSION environment variable (see section Standards conformance); it can also be enabled when POSIXLY_CORRECT is not set by using the obsolete syntax with `-pos2' present.

Scripts intended for use on standard hosts should avoid obsolete syntax and should use `-k' instead. For example, avoid `sort +2', since it might be interpreted as either `sort ./+2' or `sort -k 3'. If your script must also run on hosts that support only the obsolete syntax, it can use a test like `if sort -k 1 </dev/null >/dev/null 2>&1; then …' to decide which syntax to use.

Here are some examples to illustrate various combinations of options.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.2 shuf: Shuffling text

shuf shuffles its input by outputting a random permutation of its input lines. Each output permutation is equally likely. Synopses:

 
shuf [option]… [file]
shuf -e [option]… [arg]…
shuf -i lo-hi [option]…

shuf has three modes of operation that affect where it obtains its input lines. By default, it reads lines from standard input. The following options change the operation mode:

`-e'
`--echo'

Treat each command-line operand as an input line.

`-i lo-hi'
`--input-range=lo-hi'

Act as if input came from a file containing the range of unsigned decimal integers lohi, one per line.

shuf's other options can affect its behavior in all operation modes:

`-n lines'
`--head-count=count'

Output at most count lines. By default, all input lines are output.

`-o output-file'
`--output=output-file'

Write output to output-file instead of standard output. shuf reads all input before opening output-file, so you can safely shuffle a file in place by using commands like shuf -o F <F and cat F | shuf -o F.

`--random-source=file'

Use file as a source of random data used to determine which permutation to generate. See section Sources of random data.

`-z'
`--zero-terminated'

Delimit items with a zero byte rather than a newline (ASCII LF). I.E. treat input as items separated by ASCII NUL and terminate output items with ASCII NUL. This option can be useful in conjunction with `perl -0' or `find -print0' and `xargs -0' which do the same in order to reliably handle arbitrary file names (even those containing blanks or other special characters).

For example:

 
shuf <<EOF
A man,
a plan,
a canal:
Panama!
EOF

might produce the output

 
Panama!
A man,
a canal:
a plan,

Similarly, the command:

 
shuf -e clubs hearts diamonds spades

might output:

 
clubs
diamonds
spades
hearts

and the command `shuf -i 1-4' might output:

 
4
2
1
3

These examples all have four input lines, so shuf might produce any of the twenty-four possible permutations of the input. In general, if there are n input lines, there are n! (i.e., n factorial, or n * (n - 1) * … * 1) possible output permutations.

An exit status of zero indicates success, and a nonzero value indicates failure.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.3 uniq: Uniquify files

uniq writes the unique lines in the given `input', or standard input if nothing is given or for an input name of `-'. Synopsis:

 
uniq [option]… [input [output]]

By default, uniq prints its input lines, except that it discards all but the first of adjacent repeated lines, so that no output lines are repeated. Optionally, it can instead discard lines that are not repeated, or all repeated lines.

The input need not be sorted, but repeated input lines are detected only if they are adjacent. If you want to discard non-adjacent duplicate lines, perhaps you want to use sort -u. See section sort: Sort text files.

Comparisons honor the rules specified by the LC_COLLATE locale category.

If no output file is specified, uniq writes to standard output.

The program accepts the following options. Also see Common options.

`-f n'
`--skip-fields=n'

Skip n fields on each line before checking for uniqueness. Use a null string for comparison if a line has fewer than n fields. Fields are sequences of non-space non-tab characters that are separated from each other by at least one space or tab.

For compatibility uniq supports an obsolete option syntax `-n'. New scripts should use `-f n' instead.

`-s n'
`--skip-chars=n'

Skip n characters before checking for uniqueness. Use a null string for comparison if a line has fewer than n characters. If you use both the field and character skipping options, fields are skipped over first.

On older systems, uniq supports an obsolete option syntax `+n'. This obsolete behavior can be enabled or disabled with the _POSIX2_VERSION environment variable (see section Standards conformance), but portable scripts should avoid commands whose behavior depends on this variable. For example, use `uniq ./+10' or `uniq -s 10' rather than the ambiguous `uniq +10'.

`-c'
`--count'

Print the number of times each line occurred along with the line.

`-i'
`--ignore-case'

Ignore differences in case when comparing lines.

`-d'
`--repeated'

Discard lines that are not repeated. When used by itself, this option causes uniq to print the first copy of each repeated line, and nothing else.

`-D'
`--all-repeated[=delimit-method]'

Do not discard the second and subsequent repeated input lines, but discard lines that are not repeated. This option is useful mainly in conjunction with other options e.g., to ignore case or to compare only selected fields. The optional delimit-method tells how to delimit groups of repeated lines, and must be one of the following:

`none'

Do not delimit groups of repeated lines. This is equivalent to `--all-repeated' (`-D').

`prepend'

Output a newline before each group of repeated lines. With `--zero-terminated' (`-z'), use a zero byte (ASCII NUL) instead of a newline.

`separate'

Separate groups of repeated lines with a single newline. With `--zero-terminated' (`-z'), use a zero byte (ASCII NUL) instead of a newline. This is the same as using `prepend', except that no delimiter is inserted before the first group, and hence may be better suited for output direct to users.

Note that when groups are delimited and the input stream contains two or more consecutive blank lines, then the output is ambiguous. To avoid that, filter the input through `tr -s '\n'' to replace each sequence of consecutive newlines with a single newline.

This is a GNU extension.

`-u'
`--unique'

Discard the first repeated line. When used by itself, this option causes uniq to print unique lines, and nothing else.

`-w n'
`--check-chars=n'

Compare at most n characters on each line (after skipping any specified fields and characters). By default the entire rest of the lines are compared.

`-z'
`--zero-terminated'

Delimit items with a zero byte rather than a newline (ASCII LF). I.E. treat input as items separated by ASCII NUL and terminate output items with ASCII NUL. This option can be useful in conjunction with `perl -0' or `find -print0' and `xargs -0' which do the same in order to reliably handle arbitrary file names (even those containing blanks or other special characters).

An exit status of zero indicates success, and a nonzero value indicates failure.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.4 comm: Compare two sorted files line by line

comm writes to standard output lines that are common, and lines that are unique, to two input files; a file name of `-' means standard input. Synopsis:

 
comm [option]… file1 file2

Before comm can be used, the input files must be sorted using the collating sequence specified by the LC_COLLATE locale. If an input file ends in a non-newline character, a newline is silently appended. The sort command with no options always outputs a file that is suitable input to comm.

With no options, comm produces three-column output. Column one contains lines unique to file1, column two contains lines unique to file2, and column three contains lines common to both files. Columns are separated by a single TAB character.

The options `-1', `-2', and `-3' suppress printing of the corresponding columns (and separators). Also see Common options.

Unlike some other comparison utilities, comm has an exit status that does not depend on the result of the comparison. Upon normal completion comm produces an exit code of zero. If there is an error it exits with nonzero status.

If the `--check-order' option is given, unsorted inputs will cause a fatal error message. If the option `--nocheck-order' is given, unsorted inputs will never cause an error message. If neither of these options is given, wrongly sorted inputs are diagnosed only if an input file is found to contain unpairable lines. If an input file is diagnosed as being unsorted, the comm command will exit with a nonzero status (and the output should not be used).

Forcing comm to process wrongly sorted input files containing unpairable lines by specifying `--nocheck-order' is not guaranteed to produce any particular output. The output will probably not correspond with whatever you hoped it would be.

`--check-order'

Fail with an error message if either input file is wrongly ordered.

`--nocheck-order'

Do not check that both input files are in sorted order.

Other options are:

`--output-delimiter=str'

Print str between adjacent output columns, rather than the default of a single TAB character.

The delimiter str may not be empty.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.5 ptx: Produce permuted indexes

ptx reads a text file and essentially produces a permuted index, with each keyword in its context. The calling sketch is either one of:

 
ptx [option …] [file …]
ptx -G [option …] [input [output]]

The `-G' (or its equivalent: `--traditional') option disables all GNU extensions and reverts to traditional mode, thus introducing some limitations and changing several of the program's default option values. When `-G' is not specified, GNU extensions are always enabled. GNU extensions to ptx are documented wherever appropriate in this document. For the full list, see See section The GNU extensions to ptx.

Individual options are explained in the following sections.

When GNU extensions are enabled, there may be zero, one or several files after the options. If there is no file, the program reads the standard input. If there is one or several files, they give the name of input files which are all read in turn, as if all the input files were concatenated. However, there is a full contextual break between each file and, when automatic referencing is requested, file names and line numbers refer to individual text input files. In all cases, the program outputs the permuted index to the standard output.

When GNU extensions are not enabled, that is, when the program operates in traditional mode, there may be zero, one or two parameters besides the options. If there are no parameters, the program reads the standard input and outputs the permuted index to the standard output. If there is only one parameter, it names the text input to be read instead of the standard input. If two parameters are given, they give respectively the name of the input file to read and the name of the output file to produce. Be very careful to note that, in this case, the contents of file given by the second parameter is destroyed. This behavior is dictated by System V ptx compatibility; GNU Standards normally discourage output parameters not introduced by an option.

Note that for any file named as the value of an option or as an input text file, a single dash - may be used, in which case standard input is assumed. However, it would not make sense to use this convention more than once per program invocation.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.5.1 General options

`-G'
`--traditional'

As already explained, this option disables all GNU extensions to ptx and switches to traditional mode.

`--help'

Print a short help on standard output, then exit without further processing.

`--version'

Print the program version on standard output, then exit without further processing.

An exit status of zero indicates success, and a nonzero value indicates failure.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.5.2 Charset selection

As it is set up now, the program assumes that the input file is coded using 8-bit ISO 8859-1 code, also known as Latin-1 character set, unless it is compiled for MS-DOS, in which case it uses the character set of the IBM-PC. (GNU ptx is not known to work on smaller MS-DOS machines anymore.) Compared to 7-bit ASCII, the set of characters which are letters is different; this alters the behavior of regular expression matching. Thus, the default regular expression for a keyword allows foreign or diacriticized letters. Keyword sorting, however, is still crude; it obeys the underlying character set ordering quite blindly.

`-f'
`--ignore-case'

Fold lower case letters to upper case for sorting.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.5.3 Word selection and input processing

`-b file'
`--break-file=file'

This option provides an alternative (to `-W') method of describing which characters make up words. It introduces the name of a file which contains a list of characters which cannot be part of one word; this file is called the Break file. Any character which is not part of the Break file is a word constituent. If both options `-b' and `-W' are specified, then `-W' has precedence and `-b' is ignored.

When GNU extensions are enabled, the only way to avoid newline as a break character is to write all the break characters in the file with no newline at all, not even at the end of the file. When GNU extensions are disabled, spaces, tabs and newlines are always considered as break characters even if not included in the Break file.

`-i file'
`--ignore-file=file'

The file associated with this option contains a list of words which will never be taken as keywords in concordance output. It is called the Ignore file. The file contains exactly one word in each line; the end of line separation of words is not subject to the value of the `-S' option.

`-o file'
`--only-file=file'

The file associated with this option contains a list of words which will be retained in concordance output; any word not mentioned in this file is ignored. The file is called the Only file. The file contains exactly one word in each line; the end of line separation of words is not subject to the value of the `-S' option.

There is no default for the Only file. When both an Only file and an Ignore file are specified, a word is considered a keyword only if it is listed in the Only file and not in the Ignore file.

`-r'
`--references'

On each input line, the leading sequence of non-white space characters will be taken to be a reference that has the purpose of identifying this input line in the resulting permuted index. For more information about reference production, see See section Output formatting. Using this option changes the default value for option `-S'.

Using this option, the program does not try very hard to remove references from contexts in output, but it succeeds in doing so when the context ends exactly at the newline. If option `-r' is used with `-S' default value, or when GNU extensions are disabled, this condition is always met and references are completely excluded from the output contexts.

`-S regexp'
`--sentence-regexp=regexp'

This option selects which regular expression will describe the end of a line or the end of a sentence. In fact, this regular expression is not the only distinction between end of lines or end of sentences, and input line boundaries have no special significance outside this option. By default, when GNU extensions are enabled and if `-r' option is not used, end of sentences are used. In this case, this regex is imported from GNU Emacs:

 
[.?!][]\"')}]*\\($\\|\t\\|  \\)[ \t\n]*

Whenever GNU extensions are disabled or if `-r' option is used, end of lines are used; in this case, the default regexp is just:

 
\n

Using an empty regexp is equivalent to completely disabling end of line or end of sentence recognition. In this case, the whole file is considered to be a single big line or sentence. The user might want to disallow all truncation flag generation as well, through option `-F ""'. See (emacs)Regexps section `Syntax of Regular Expressions' in The GNU Emacs Manual.

When the keywords happen to be near the beginning of the input line or sentence, this often creates an unused area at the beginning of the output context line; when the keywords happen to be near the end of the input line or sentence, this often creates an unused area at the end of the output context line. The program tries to fill those unused areas by wrapping around context in them; the tail of the input line or sentence is used to fill the unused area on the left of the output line; the head of the input line or sentence is used to fill the unused area on the right of the output line.

As a matter of convenience to the user, many usual backslashed escape sequences from the C language are recognized and converted to the corresponding characters by ptx itself.

`-W regexp'
`--word-regexp=regexp'

This option selects which regular expression will describe each keyword. By default, if GNU extensions are enabled, a word is a sequence of letters; the regexp used is `\w+'. When GNU extensions are disabled, a word is by default anything which ends with a space, a tab or a newline; the regexp used is `[^ \t\n]+'.

An empty regexp is equivalent to not using this option. See (emacs)Regexps section `Syntax of Regular Expressions' in The GNU Emacs Manual.

As a matter of convenience to the user, many usual backslashed escape sequences, as found in the C language, are recognized and converted to the corresponding characters by ptx itself.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.5.4 Output formatting

Output format is mainly controlled by the `-O' and `-T' options described in the table below. When neither `-O' nor `-T' are selected, and if GNU extensions are enabled, the program chooses an output format suitable for a dumb terminal. Each keyword occurrence is output to the center of one line, surrounded by its left and right contexts. Each field is properly justified, so the concordance output can be readily observed. As a special feature, if automatic references are selected by option `-A' and are output before the left context, that is, if option `-R' is not selected, then a colon is added after the reference; this nicely interfaces with GNU Emacs next-error processing. In this default output format, each white space character, like newline and tab, is merely changed to exactly one space, with no special attempt to compress consecutive spaces. This might change in the future. Except for those white space characters, every other character of the underlying set of 256 characters is transmitted verbatim.

Output format is further controlled by the following options.

`-g number'
`--gap-size=number'

Select the size of the minimum white space gap between the fields on the output line.

`-w number'
`--width=number'

Select the maximum output width of each final line. If references are used, they are included or excluded from the maximum output width depending on the value of option `-R'. If this option is not selected, that is, when references are output before the left context, the maximum output width takes into account the maximum length of all references. If this option is selected, that is, when references are output after the right context, the maximum output width does not take into account the space taken by references, nor the gap that precedes them.

`-A'
`--auto-reference'

Select automatic references. Each input line will have an automatic reference made up of the file name and the line ordinal, with a single colon between them. However, the file name will be empty when standard input is being read. If both `-A' and `-r' are selected, then the input reference is still read and skipped, but the automatic reference is used at output time, overriding the input reference.

`-R'
`--right-side-refs'

In the default output format, when option `-R' is not used, any references produced by the effect of options `-r' or `-A' are placed to the far right of output lines, after the right context. With default output format, when the `-R' option is specified, references are rather placed at the beginning of each output line, before the left context. For any other output format, option `-R' is ignored, with one exception: with `-R' the width of references is not taken into account in total output width given by `-w'.

This option is automatically selected whenever GNU extensions are disabled.

`-F string'
`--flac-truncation=string'

This option will request that any truncation in the output be reported using the string string. Most output fields theoretically extend towards the beginning or the end of the current line, or current sentence, as selected with option `-S'. But there is a maximum allowed output line width, changeable through option `-w', which is further divided into space for various output fields. When a field has to be truncated because it cannot extend beyond the beginning or the end of the current line to fit in, then a truncation occurs. By default, the string used is a single slash, as in `-F /'.

string may have more than one character, as in `-F ...'. Also, in the particular case when string is empty (`-F ""'), truncation flagging is disabled, and no truncation marks are appended in this case.

As a matter of convenience to the user, many usual backslashed escape sequences, as found in the C language, are recognized and converted to the corresponding characters by ptx itself.

`-M string'
`--macro-name=string'

Select another string to be used instead of `xx', while generating output suitable for nroff, troff or TeX.

`-O'
`--format=roff'

Choose an output format suitable for nroff or troff processing. Each output line will look like:

 
.xx "tail" "before" "keyword_and_after" "head" "ref"

so it will be possible to write a `.xx' roff macro to take care of the output typesetting. This is the default output format when GNU extensions are disabled. Option `-M' can be used to change `xx' to another macro name.

In this output format, each non-graphical character, like newline and tab, is merely changed to exactly one space, with no special attempt to compress consecutive spaces. Each quote character: " is doubled so it will be correctly processed by nroff or troff.

`-T'
`--format=tex'

Choose an output format suitable for TeX processing. Each output line will look like:

 
\xx {tail}{before}{keyword}{after}{head}{ref}

so it will be possible to write a \xx definition to take care of the output typesetting. Note that when references are not being produced, that is, neither option `-A' nor option `-r' is selected, the last parameter of each \xx call is inhibited. Option `-M' can be used to change `xx' to another macro name.

In this output format, some special characters, like $, %, &, # and _ are automatically protected with a backslash. Curly brackets {, } are protected with a backslash and a pair of dollar signs (to force mathematical mode). The backslash itself produces the sequence \backslash{}. Circumflex and tilde diacritical marks produce the sequence ^\{ } and ~\{ } respectively. Other diacriticized characters of the underlying character set produce an appropriate TeX sequence as far as possible. The other non-graphical characters, like newline and tab, and all other characters which are not part of ASCII, are merely changed to exactly one space, with no special attempt to compress consecutive spaces. Let me know how to improve this special character processing for TeX.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.5.5 The GNU extensions to ptx

This version of ptx contains a few features which do not exist in System V ptx. These extra features are suppressed by using the `-G' command line option, unless overridden by other command line options. Some GNU extensions cannot be recovered by overriding, so the simple rule is to avoid `-G' if you care about GNU extensions. Here are the differences between this program and System V ptx.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.6 tsort: Topological sort

tsort performs a topological sort on the given file, or standard input if no input file is given or for a file of `-'. For more details and some history, see tsort: Background. Synopsis:

 
tsort [option] [file]

tsort reads its input as pairs of strings, separated by blanks, indicating a partial ordering. The output is a total ordering that corresponds to the given partial ordering.

For example

 
tsort <<EOF
a b c
d
e f
b c d e
EOF

will produce the output

 
a
b
c
d
e
f

Consider a more realistic example. You have a large set of functions all in one file, and they may all be declared static except one. Currently that one (say main) is the first function defined in the file, and the ones it calls directly follow it, followed by those they call, etc. Let's say that you are determined to take advantage of prototypes, so you have to choose between declaring all of those functions (which means duplicating a lot of information from the definitions) and rearranging the functions so that as many as possible are defined before they are used. One way to automate the latter process is to get a list for each function of the functions it calls directly. Many programs can generate such lists. They describe a call graph. Consider the following list, in which a given line indicates that the function on the left calls the one on the right directly.

 
main parse_options
main tail_file
main tail_forever
tail_file pretty_name
tail_file write_header
tail_file tail
tail_forever recheck
tail_forever pretty_name
tail_forever write_header
tail_forever dump_remainder
tail tail_lines
tail tail_bytes
tail_lines start_lines
tail_lines dump_remainder
tail_lines file_lines
tail_lines pipe_lines
tail_bytes xlseek
tail_bytes start_bytes
tail_bytes dump_remainder
tail_bytes pipe_bytes
file_lines dump_remainder
recheck pretty_name

then you can use tsort to produce an ordering of those functions that satisfies your requirement.

 
example$ tsort call-graph | tac
dump_remainder
start_lines
file_lines
pipe_lines
xlseek
start_bytes
pipe_bytes
tail_lines
tail_bytes
pretty_name
write_header
tail
recheck
parse_options
tail_file
tail_forever
main

tsort detects any cycles in the input and writes the first cycle encountered to standard error.

Note that for a given partial ordering, generally there is no unique total ordering. In the context of the call graph above, the function parse_options may be placed anywhere in the list as long as it precedes main.

The only options are `--help' and `--version'. See section Common options.

An exit status of zero indicates success, and a nonzero value indicates failure.


[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

7.6.1 tsort: Background

tsort exists because very early versions of the Unix linker processed an archive file exactly once, and in order. As ld read each object in the archive, it decided whether it was needed in the program based on whether it defined any symbols which were undefined at that point in the link.

This meant that dependencies within the archive had to be handled specially. For example, scanf probably calls read. That means that in a single pass through an archive, it was important for scanf.o to appear before read.o, because otherwise a program which calls scanf but not read might end up with an unexpected unresolved reference to read.

The way to address this problem was to first generate a set of dependencies of one object file on another. This was done by a shell script called lorder. The GNU tools don't provide a version of lorder, as far as I know, but you can still find it in BSD distributions.

Then you ran tsort over the lorder output, and you used the resulting sort to define the order in which you added objects to the archive.

This whole procedure has been obsolete since about 1980, because Unix archives now contain a symbol table (traditionally built by ranlib, now generally built by ar itself), and the Unix linker uses the symbol table to effectively make multiple passes over an archive file.

Anyhow, that's where tsort came from. To solve an old problem with the way the linker handled archive files, which has since been solved in different ways.


[ << ] [ >> ]           [Top] [Contents] [Index] [ ? ]

This document was generated on January, 20 2010 using texi2html 1.76.