prepend.sh : insert text above given line number (the first by default) or pattern. Bash script.

prepend.sh

#!/usr/bin/env bash
#              bash 4.1.5(1)     Linux Ubuntu 10.04           Date : 2011-12-14
#
# _______________|  prepend : insert text above given line number or pattern.
#
#           Usage:  prepend  ["text"] [filename=stdin] [linenum=1 OR pattern]
#
#         Example:  prepend "TEST1\nTEST2" foo 3
#                   #  insert two test lines above the third line in file foo.
#                   sort foo | prepend "Sorted result:"
#                   #  insert title at the top of incoming pipe.
#
#    Dependencies:  sed
#
#    N.B.  -  Within "text" one can use \n for NEWLINE.
#    Third argument can be a sed PATTERN, e.g. '/^Section/'
#       and insertion would occur above all lines with such pattern.
#       Negation after pattern might be useful, e.g. '/^Section/!'


#  CHANGE LOG  get LATEST version from https://bitbucket.org/rsvp/gists/src
#
#  2011-12-14  Use virtual memory as temporary file.
#  2011-12-13  First version could have done something like this:
#                      cat <(echo -e "text") filename
#                 but that works as insertion only above first line,
#                 and we would have to rename the file anyways.
#                 New design also works with PIPES.

#           _____ Prelims
set -u
#   ^ unbound (i.e. unassigned) variables shall be errors.
#           Example of default assignment:    arg1=${1:-'foo'}
set -e
#   ^ error checking :: Highly Recommended (caveat:  you can't check $? later).  
#
# _______________     ::  BEGIN  Script ::::::::::::::::::::::::::::::::::::::::

filename=${2:-'-'}
#             ^stdin as default. 
arg3=${3:-'1'}
#         ^default is the first line of the file.
#     ^third argument for specifying line number or sed pattern.

tmpf='/dev/shm/prepend.tmp'
#    ^virtual memory, otherwise one could use on disk: '/tmp/prepend.tmp'


#  We use sed for the MAIN job, insertion:
sed "${arg3}i\\$1"  "$filename"  > $tmpf
#            ^^tricky double backslash because command is double quoted.


if [ "$filename" = '-' ] ; then
     #             ^stdin as default entails different output behavior:
     cat $tmpf
     #   show the modified file (which is expected pipe behavior).
else
     mv  $tmpf "$filename"
     #   show nothing, but properly rename the modified file.
fi


#  clean-up
rm -f $tmpf


exit 0
# _______________ EOS ::  END of Script ::::::::::::::::::::::::::::::::::::::::

#  vim: set fileencoding=utf-8 ff=unix tw=78 ai syn=sh :