4.31. How do I export or pass variables back into the environment?

4.31.1. - on Unix platforms

Suppose that line #1, word #2 of the file 'terminals' contains a value to be put in your TERM environment variable. Sed cannot export variables directly to the shell, but it can pass strings to shell commands. To set a variable in the Bourne shell:

       TERM=`sed 's/^[^ ][^ ]* \([^ ][^ ]*\).*/\1/;q' terminals`;
       export TERM

If the second word were "Wyse50", this would send the shell command "TERM=Wyse50".

4.31.2. - on MS-DOS or 4DOS platforms

Sed cannot directly manipulate the environment. Under DOS, only batch files (.BAT) can do this, using the SET instruction, since they are run directly by the command shell. Under 4DOS, special 4DOS commands (such as ESET) can also alter the environment.

Under DOS or 4DOS, sed can select a word and pass it to the SET command. Suppose you want the 1st word of the 2nd line of MY.DAT put into an environment variable named %PHONE%. You might do this:

       @echo off
       sed -n "2 s/^\([^ ][^ ]*\) .*/SET PHONE=\1/p;3q" MY.DAT > GO_.BAT
       call GO_.BAT
       echo The environment variable for PHONE is %PHONE%
       :: cleanup
       del GO_.BAT

The sed script assumes that the first character on the 2nd line is not a space and uses grouping \(...\) to save the first string of non-space characters as \1 for the RHS. In writing any batch files, make sure that output filenames such as GO_.BAT don't overwrite preexisting files of the same name.