Advanced Bash−Scripting Guide

Perl, sed, and awk have far superior string parsing facilities. A short sed or awk "subroutine" within a script
(see Section 34.2) is an attractive alternative to using expr.
See Section 9.2 for more on string operations.
12.3. Time / Date Commands
Time/date and timing
Advanced Bash−Scripting Guide
date
Simply invoked, date prints the date and time to stdout. Where this command gets interesting is in
its formatting and parsing options.
Example 12−7. Using date
#!/bin/bash
# Exercising the 'date' command
echo "The number of days since the year's beginning is `date +%j`."
# Needs a leading '+' to invoke formatting.
# %j gives day of year.
echo "The number of seconds elapsed since 01/01/1970 is `date +%s`."
# %s yields number of seconds since "UNIX epoch" began,
#+ but how is this useful?
prefix=temp
suffix=`eval date +%s` # The "+%s" option to 'date' is GNU−specific.
filename=$prefix.$suffix
echo $filename
# It's great for creating "unique" temp filenames,
#+ even better than using $$.
# Read the 'date' man page for more formatting options.
exit 0
The −u option gives the UTC (Universal Coordinated Time).
bash$ date
Fri Mar 29 21:07:39 MST 2002
bash$ date −u
Sat Mar 30 04:07:42 UTC 2002
zdump
Echoes the time in a specified time zone.
bash$ zdump EST
EST Tue Sep 18 22:09:22 2001 EST
time
Chapter 12. External Filters, Programs and Commands 158