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88 lines
2.2 KiB
Plaintext
88 lines
2.2 KiB
Plaintext
====== Generate code with own arguments properly quoted ======
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---- dataentry snipplet ----
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snipplet_tags: arguments, quoting, escaping, wrapper
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LastUpdate_dt: 2010-07-31
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Contributors: Jan Schampera
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type: snipplet
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----
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^ Keywords: | arguments,escape,quote,wrapper,generate |
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^ Contributor: | self |
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There are situations where Bash code needs to generate Bash code. A script that writes out another script the user or cron may start, for example.
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The general issue is easy, just write out text to the file.
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A specific detail of it is tricky: If the generated script needs to call a command using the arguments the first original script got, you have problem in writing out the correct code.
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I.e. if you run your generator script like
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<code>./myscript "give me 'some' water"</code>
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then this script should generate code that looks like
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<code>echo give me 'some' water"</code>
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you need correct escapes or quotes to not generate shell special characters out of normal text (like embedded dollar signs ''$'').
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**__Solution:__**
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A loop over the own arguments that writes out properly quoted/escaped code to the generated script file
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There are two (maybe more) easy options:
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* writing out singlequoted strings and handle the embedded singlequotes
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* the [[commands:builtin:printf | printf command]] knows the ''%q'' format specification, which will print a string (like ''%s'' does), but with all shell special characters escaped
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===== Using singlequoted string =====
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<code>
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#!/bin/bash
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# first option:
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# generate singlequoted strings out of your own arguments and handle embedded singlequotes
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# here to call 'echo' in the generated script
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{
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printf "#!/bin/bash\n\n"
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printf "echo "
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for arg; do
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arg=${arg/\'/\'\\\'\'}
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printf "'%s' " "${arg}"
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done
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printf "\n"
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} >s2
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</code>
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The generated script will look like:
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<code>
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#!/bin/bash
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echo 'fir$t' 'seco "ond"' 'thir'\''d'
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</code>
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===== Using printf =====
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The second method is easier, though more or less Bash-only (due to the ''%q'' in printf):
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<code>
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#!/bin/bash
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{
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printf "#!/bin/bash\n\n"
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printf "echo "
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for arg; do
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printf '%q ' "$arg"
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done
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printf "\n"
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} >s2
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</code>
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The generated script will look like:
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<code>
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#!/bin/bash
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echo fir\$t seco\ \"ond\" thir\'d
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</code>
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