Question

4

Using read without losing the TAB

rated 0 times [ 4] [ 0] / answers: 1 / hits: 3569 / 2 Years ago, wed, august 17, 2022, 5:49:26

Im using read in a while loop to automatically change a makefile after download.

Here is part of the script,

    while read a; do

    if [[ "$a" = "FCOMPL=g77" ]]

    then echo "FCOMPL=gfortran" >> makefile

    elif [[ "$a" = "FFLAGC=-Wall -O" ]]

    then echo "FFLAGC=-Wall -O -fno-backslash" >> makefile

    else

    echo $a >> makefile

    fi

    done <makefile.orig

The problem is that I lose the tabulation.

Any idea of how I can avoid that?

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istmasted

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answered 2 Years ago calcur · Accepted Answer

Instead of using bash to do the task, you could learn sed:

sed -e 's/^FCOMPL=g77$/FCOMPL=gfortran/' 

    -e '/^FFLAGC=-Wall -O$/s/$/ -fno-backslash/' makefile.orig > makefile

Each -e gives sed a command to perform. In this case (1st -e), the s command performs a substitution: s/foo/bar/ replaces the 1st occurrence of foo on each line by bar. To be sure we work on complete line, I added ^ (beginning of the line) and $ (end of the line).

You can prefix a command by a selector. In this case (2nd -e), the s command is applied only to a line matching ^FFLAGC=-Wall -O$.

You could even use the -i flag to replace the file:

sed -i -e 's/^FCOMPL=g77$/FCOMPL=gfortran/' 

       -e '/^FFLAGC=-Wall -O$/s/$/ -fno-backslash/' makefile