01-30-2020
This function is quite well commented, it basically uses the tail command to print the last MAX_LENGTH ($2) lines of FILE ($1) these are stored in a temporary file (name generated by the mktmp command) the contents of this temporary file is then copied back over the original file and the temporary file removed.
All the operations performed are checked to ensure they have a success exit code before moving onto the next step.
Which particular part of the function you are having trouble understanding?
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LEARN ABOUT DEBIAN
tempfile
TEMPFILE(1) General Commands Manual TEMPFILE(1)
NAME
tempfile - create a temporary file in a safe manner
SYNOPSIS
tempfile [-d DIR] [-p STRING] [-s STRING] [-m MODE] [-n FILE] [--directory=DIR] [--prefix=STRING] [--suffix=STRING] [--mode=MODE]
[--name=FILE] [--help] [--version]
DESCRIPTION
tempfile creates a temporary file in a safe manner. It uses tempnam(3) to choose the name and opens it with O_RDWR | O_CREAT | O_EXCL.
The filename is printed on standard output. See tempnam(3) for the actual steps involved in directory selection.
The directory in which to create the file might be searched for in this order (but refer to tempnam(3) for authoritative answers):
a) In case the environment variable TMPDIR exists and contains the name of an appropriate directory, that is used.
b) Otherwise, if the --directory argument is specified and appropriate, it is used.
c) Otherwise, P_tmpdir (as defined in <stdio.h>) is used when appropriate.
d) Finally an implementation-defined directory (/tmp) may be used.
OPTIONS
-d, --directory DIR
Place the file in DIR.
-m, --mode MODE
Open the file with MODE instead of 0600.
-n, --name FILE
Use FILE for the name instead of tempnam(3). The options -d, -p, and -s are ignored if this option is given.
-p, --prefix STRING
Use up to five letters of STRING to generate the name.
-s, --suffix STRING
Generate the file with STRING as the suffix.
--help Print a usage message on standard output and exit successfully.
--version
Print version information on standard output and exit successfully.
RETURN VALUES
An exit status of 0 means the temporary file was created successfully. Any other exit status indicates an error.
BUGS
Exclusive creation is not guaranteed when creating files on NFS partitions. tempfile cannot make temporary directories. tempfile is dep-
recated; you should use mktemp(1) instead.
EXAMPLE
#!/bin/sh
#[...]
t=$(tempfile) || exit
trap "rm -f -- '$t'" EXIT
#[...]
rm -f -- "$t"
trap - EXIT
exit
SEE ALSO
tempnam(3), mktemp(1)
Debian 27 Jun 2012 TEMPFILE(1)