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Asked: 2026-05-26T05:46:47+00:00

I’ve written a function in zsh to find and replace a specific number with

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I’ve written a function in zsh to find and replace a specific number with a keyword that I’ll use later on in a larger script. Here’s what I’ve got:

function replace_metal() {
for file in "$@"; do
    [ -f "$file" ] && mv $file $file.old

    # replace metal
    awk '/^28\s/ { gsub(/28\s/, "METAL") }; { print }' $file.old > $file

    # remove temporary files
    rm -f $file.old
done
}

The awk portion works fine when I run it on the command line but while in the script, it fails to parse the file and replace the number with the keyword. I’m not sure why it fails. I’ve written a function that is similar that works without any trouble:

function fix_filename() {
for file in "$@"; do
    [ -f "$file" ] && mv $file $file.old

    # fix filename
    awk '{ gsub(/myFileName/,FILENAME); print }' $file.old > $file.tmp

    # clean up filename
    awk '{ gsub(/.gjf.old/,""); print }' $file.tmp > $file

    # remove temporary files
    rm -f $file.old $file.tmp
done
}

I’m especially confused as to why awk won’t work in the replace_metal function but will on the command line. If anyone can explain that, I’d really appreciate it.

Here’s an example portion of a file that I’d run this script on. They are cartesian coordinates for a molecular geometry program I use.

6 4.387152 -0.132561 1.145384
6 4.435130 0.035315 -0.261758
6 3.241800 0.069735 -1.002575
7 2.023205 -0.053248 -0.382329
6 1.948032 -0.217668 0.977856
6 3.120408 -0.260395 1.759133
8 0.936529 -0.001059 -1.144164
28 -0.810634 -0.374713 -0.376819
7 -1.066408 1.593331 -0.221421
6 -2.101594 2.162030 0.386527
6 -3.220999 1.475281 0.925467
7 -2.581803 -0.796964 0.180331
6 -3.412540 0.082878 0.747753
6 -0.299269 -2.264241 -0.449077
1 5.304344 -0.163663 1.737743
1 5.382399 0.136858 -0.794636
1 3.185977 0.187888 -2.085134
1 0.932373 -0.311671 1.366224
1 3.017555 -0.393258 2.837678
1 -2.114644 3.263364 0.463786
1 -4.007715 2.050042 1.415626
1 -4.379471 -0.313239 1.099097
1 -0.572811 -2.828718 0.461055
1 0.789786 -2.379489 -0.603095
1 -0.795666 -2.747919 -1.311858
6 -3.146815 -2.155894 0.046938
1 -2.990568 -2.540510 -0.972499
1 -2.672661 -2.865421 0.746200
1 -4.233217 -2.149944 0.247135
6 -0.086130 2.536630 -0.792152
1 0.886270 2.480474 -0.265799
1 0.102603 2.306402 -1.853394
1 -0.445050 3.580750 -0.720938

Items in the first column are the only things that can be changed. Items in the other three columns should not ever change.

Thanks for your help!

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1 Answer

  1. Editorial Team

    the problem is the escaping of the “\”-character. Experiment with “\\s” or even “\\\\s”. If you don’t run the script directly, the “\”-character is evaluated two times: at first by the shell and then by awk. Anyway, you solution is way too complicated.

    Try:

    sed -i "s/^28 /METAL/" file

    sed -i means substitute in place, so you don’t have to copy the file “file” to “file.old” and then back again to “file”.

    Zsh has a built-in function to escape strings:

    f="to be escaped"
print ${(q)f}

    HTH Chris

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