Advanced Bash−Scripting Guide

# cmp −s $1 $2 has same result ("−s" silent flag to "cmp")
# Thank you Anders Gustavsson for pointing this out.
#
# Also works with 'diff', i.e., diff $1 $2 &> /dev/null
if [ $? −eq 0 ]
# Test exit status of "cmp" command.
then
echo "File \"$1\" is identical to file \"$2\"."
else
echo "File \"$1\" differs from file \"$2\"."
fi
exit 0
Advanced Bash−Scripting Guide
comm
Use zcmp on gzipped files.
Versatile file comparison utility. The files must be sorted for this to be useful.
Utilities
comm −options first−file second−file
comm file−1 file−2 outputs three columns:
◊ column 1 = lines unique to file−1
◊ column 2 = lines unique to file−2
◊ column 3 = lines common to both.
The options allow suppressing output of one or more columns.
◊ −1 suppresses column 1
◊ −2 suppresses column 2
◊ −3 suppresses column 3
◊ −12 suppresses both columns 1 and 2, etc.
basename
Strips the path information from a file name, printing only the file name. The construction
basename $0 lets the script know its name, that is, the name it was invoked by. This can be used
for "usage" messages if, for example a script is called with missing arguments:
echo "Usage: `basename $0` arg1 arg2 ... argn"
dirname
Strips the basename from a filename, printing only the path information.
basename and dirname can operate on any arbitrary string. The argument does not
need to refer to an existing file, or even be a filename for that matter (see Example
A−8).
Example 12−28. basename and dirname
#!/bin/bash
a=/home/bozo/daily−journal.txt
Chapter 12. External Filters, Programs and Commands 186