Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
exit $E_WRONGARGS
fi
filename=$1
column_number=$2
# Passing shell variables to the awk part of the script is a bit tricky.
# See the awk documentation for more details.
# A multi−line awk script is invoked by awk ' ..... '
# Begin awk script.
# −−−−−−−−−−−−−−−−−−−−−−−−−−−−−
awk '
{ total += $'"${column_number}"'
}
END {
print total
}
' "$filename"
# −−−−−−−−−−−−−−−−−−−−−−−−−−−−−
# End awk script.
# It may not be safe to pass shell variables to an embedded awk script,
# so Stephane Chazelas proposes the following alternative:
# −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
# awk −v column_number="$column_number" '
# { total += $column_number
# }
# END {
# print total
# }' "$filename"
# −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
exit 0
For those scripts needing a single do−it−all tool, a Swiss army knife, there is Perl. Perl combines the
capabilities of sed and awk, and throws in a large subset of C, to boot. It is modular and contains support for
everything ranging from object−oriented programming up to and including the kitchen sink. Short Perl scripts
lend themselves to embedding in shell scripts, and there may even be some substance to the claim that Perl
can totally replace shell scripting (though the author of this document remains skeptical).
Example 34−4. Perl embedded in a Bash script
#!/bin/bash
# Shell commands may precede the Perl script.
echo "This precedes the embedded Perl script within \"$0\"."
echo "==============================================================="
perl −e 'print "This is an embedded Perl script.\n";'
# Like sed, Perl also uses the "−e" option.
echo "==============================================================="
Chapter 34. Miscellany 339