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bashquotes
Robin Vogel
Robin Vogel

Reputation: 159

Small question about export and $() double quotes

When I write export X="test" in a file test.sh and do $(cat test.sh) in shell quote stay, i.e. echo $X gives "test" whereas export X="test" directly in shell makes quotes disappear, i.e. echo $X gives test why ?

I seem to be executing the same code and it has been messing with my paths :)

Upvotes: 1

Views: 357

Answers (2)

Robin Vogel
Robin Vogel

Reputation: 159

Given a file test.sh that contains the phrase export X="test" the command cat test.sh outputs the string with escaped double-quotes export X=\"test\" which evaluates when printed in the bash console as export X="test".

Which is why I was under the impression that I executed the same code, however in the first case I was affecting \"test\" to X while in the second I was affecting test to it.

The solution that I first used and then saw elsewhere is to pipe the output of cat to sed 's/"//g', note the single quotes ' instead of double quotes ".

Thanks to Hendrik Prinsloo for the reference above.

Upvotes: 0

chepner
chepner

Reputation: 531055

The difference between the two is quote removal. From the man page,

Quote Removal

After the preceding expansions, all unquoted occurrences of the characters \, ', and " that did not result from one of the above expansions are removed.

In $(cat test.sh), the eventual command contains unquoted " characters that did result from a command substitution. The command substitution produced export X="test", which splits into the command word export and its literal argument X="test".

In export X="test", the command is again export with an argument X="test", but those quotes are unquoted and were not produced by any expansions, so they are removed. The result is the command export receiving X=test (not X="test") as its argument.

Each export command then splits its argument on the =, seeing X as the variable to define. One sees a right-hand side of test to use as a value, the other sees "test" to use as the value, resulting in the different assignments that you observed.

Upvotes: 1

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