The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group


csplit - split files based on context


csplit [-ks] [-f prefix] [-n number] file arg...


The csplit utility shall read the file named by the file operand, write all or part of that file into other files as directed by the arg operands, and write the sizes of the files.


The csplit utility shall conform to XBD Utility Syntax Guidelines.

The following options shall be supported:

-f  prefix
Name the created files prefix 00, prefix 01, ..., prefixn. The default is xx00... xx n. If the prefix argument would create a filename exceeding {NAME_MAX} bytes, an error shall result, csplit shall exit with a diagnostic message, and no files shall be created.
Leave previously created files intact. By default, csplit shall remove created files if an error occurs.
-n  number
Use number decimal digits to form filenames for the file pieces. The default shall be 2.
Suppress the output of file size messages.


The following operands shall be supported:

The pathname of a text file to be split. If file is '-', the standard input shall be used.

Each arg operand can be one of the following:

A file shall be created using the content of the lines from the current line up to, but not including, the line that results from the evaluation of the regular expression with offset, if any, applied. The regular expression rexp shall follow the rules for basic regular expressions described in XBD Basic Regular Expressions. The application shall use the sequence "\/" to specify a <slash> character within the rexp. The optional offset shall be a positive or negative integer value representing a number of lines. A positive integer value can be preceded by '+'. If the selection of lines from an offset expression of this type would create a file with zero lines, or one with greater than the number of lines left in the input file, the results are unspecified. After the section is created, the current line shall be set to the line that results from the evaluation of the regular expression with any offset applied. If the current line is the first line in the file and a regular expression operation has not yet been performed, the pattern match of rexp shall be applied from the current line to the end of the file. Otherwise, the pattern match of rexp shall be applied from the line following the current line to the end of the file.
Equivalent to /rexp/[offset], except that no file shall be created for the selected section of the input file. The application shall use the sequence "\%" to specify a <percent-sign> character within the rexp.
Create a file from the current line up to (but not including) the line number line_no. Lines in the file shall be numbered starting at one. The current line becomes line_no.
Repeat operand. This operand can follow any of the operands described previously. If it follows a rexp type operand, that operand shall be applied num more times. If it follows a line_no operand, the file shall be split every line_no lines, num times, from that point.

An error shall be reported if an operand does not reference a line between the current position and the end of the file.


See the INPUT FILES section.


The input file shall be a text file.


The following environment variables shall affect the execution of csplit:

Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
If set to a non-empty string value, override the values of all the other internationalization variables.
Determine the locale for the behavior of ranges, equivalence classes, and multi-character collating elements within regular expressions.
Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files) and the behavior of character classes within regular expressions.
Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
[XSI] [Option Start] Determine the location of message catalogs for the processing of LC_MESSAGES. [Option End]


If the -k option is specified, created files shall be retained. Otherwise, the default action occurs.


Unless the -s option is used, the standard output shall consist of one line per file created, with a format as follows:

"%d\n", <file size in bytes>


The standard error shall be used only for diagnostic messages.


The output files shall contain portions of the original input file; otherwise, unchanged.




The following exit values shall be returned:

Successful completion.
An error occurred.


By default, created files shall be removed if an error occurs. When the -k option is specified, created files shall not be removed if an error occurs.

The following sections are informative.




  1. This example creates four files, cobol00... cobol03:

    csplit -f cobol file '/procedure division/' /par5./ /par16./

    After editing the split files, they can be recombined as follows:

    cat cobol0[0-3] > file

    Note that this example overwrites the original file.

  2. This example would split the file after the first 99 lines, and every 100 lines thereafter, up to 9999 lines; this is because lines in the file are numbered from 1 rather than zero, for historical reasons:

    csplit -k file  100  {99}
  3. Assuming that prog.c follows the C-language coding convention of ending routines with a '}' at the beginning of the line, this example creates a file containing each separate C routine (up to 21) in prog.c:

    csplit -k prog.c '%main(%'  '/^}/+1' {20}


The -n option was added to extend the range of filenames that could be handled.

Consideration was given to adding a -a flag to use the alphabetic filename generation used by the historical split utility, but the functionality added by the -n option was deemed to make alphabetic naming unnecessary.




sed, split

XBD Environment Variables, Basic Regular Expressions, Utility Syntax Guidelines


First released in Issue 2.

Issue 5

The FUTURE DIRECTIONS section is added.

Issue 6

This utility is marked as part of the User Portability Utilities option.

The APPLICATION USAGE section is added.

The description of regular expression operands is changed to align with the IEEE P1003.2b draft standard.

The normative text is reworded to avoid use of the term "must" for application requirements.

Issue 7

The csplit utility is moved from the User Portability Utilities option to the Base. User Portability Utilities is now an option for interactive utilities.

SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.

The SYNOPSIS and OPERANDS sections are revised to use a single arg to split a file into two pieces.

End of informative text.


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