Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
# interactive
...
fi
Alternatively, the script can test for the presence of option "i" in the $− flag.
case $− in
*i*) # interactive shell
;;
*) # non−interactive shell
;;
# (Courtesy of "UNIX F.A.Q.," 1993)
Scripts may be forced to run in interactive mode with the −i option or with a #!/bin/bash −i
header. Be aware that this can cause erratic script behavior or show error messages even when no error is
present.
34.2. Shell Wrappers
A "wrapper" is a shell script that embeds a system command or utility, that saves a set of parameters passed to
that command. Wrapping a script around a complex command line simplifies invoking it. This is expecially
useful with sed and awk.
A sed or awk script would normally be invoked from the command line by a sed −e 'commands' or
awk 'commands'. Embedding such a script in a Bash script permits calling it more simply, and makes it
"reusable". This also enables combining the functionality of sed and awk, for example piping the output of a
set of sed commands to awk. As a saved executable file, you can then repeatedly invoke it in its original form
or modified, without the inconvenience of retyping it on the command line.
Example 34−1. shell wrapper
#!/bin/bash
# This is a simple script that removes blank lines from a file.
# No argument checking.
#
# You might wish to add something like:
# if [ −z "$1" ]
# then
# echo "Usage: `basename $0` target−file"
# exit 65
# fi
# Same as
# sed −e '/^$/d' filename
# invoked from the command line.
sed −e /^$/d "$1"
# The '−e' means an "editing" command follows (optional here).
# '^' is the beginning of line, '$' is the end.
# This match lines with nothing between the beginning and the end,
#+ blank lines.
Chapter 34. Miscellany 337