i have a homework to print the header of a shell script as help option using sed
The shell script (the correct answer from prof)
#---------------------------------------------------------------------
# File-name: <script1.sh>
# Language: bash script
# Project: Shell Script Programming Class
# Description: xyz
# Author: iamgroot
#---------------------------------------------------------------------
if [ "$1" == '-h' ] ; then
echo Help:
sed -n '/File\-name/,/A\uthor/p' "$0" | sed "s/^#//g"
exit 0
fi
The output
Help:
File-name: <script1.sh>
Language: bash script
Project: Shell Script Programming Class
Description: xyz
Author: iamgroot
I dont understand why there is \
before -name
and before uthor
(row 10 shell script)
Also why there is "$0"
(the same row)? Any help would be appreciated
To illustrate my answer in comments:
$ cat f
#---------------------------------------------------------------------
# File-name: <script1.sh>
# Language: bash script
# Project: Shell Script Programming Class
# Description: xyz
# Author: iamgroot
#---------------------------------------------------------------------
$ sed -n '/File\-name/,/A\uthor/p' f
# File-name: <script1.sh>
# Language: bash script
# Project: Shell Script Programming Class
# Description: xyz
# Author: iamgroot
$ sed -n '/File-name/,/Author/p' f
# File-name: <script1.sh>
# Language: bash script
# Project: Shell Script Programming Class
# Description: xyz
# Author: iamgroot
The \
before -name
is not needed at all, and probably leads to undefined behaviour. It is put there to prevent a second match (for the string File-name
) in the sed
line, but that is not an appropriate method to do the job. A plausible method could have been:
$ cat testscript
#!/bin/bash
#---------------------------------------------------------------------
# File-name: <script1.sh>
# Language: bash script
# Project: Shell Script Programming Class
# Description: xyz
# Author: iamgroot
#---------------------------------------------------------------------
if [ "$1" = '-h' ] ; then
echo Help:
sed -n '/^#[[:blank:]]*File-name/,/^#[[:blank:]]*Author/{s/^#//p;}' "$0"
exit 0
fi
$./testscript -h
Help:
File-name: <script1.sh>
Language: bash script
Project: Shell Script Programming Class
Description: xyz
Author: iamgroot
However, I'd change the sed
line to something like this:
sed -n -e '/^#--*$/!d' -e ':a' -e 'n; /^#--*$/q; s/^#//p; ba' "$0"
This will print out the lines between #--...--
s, stripping the leading #
s out.
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