CODEWITHSUNDEEP
perlbashreplace
Goulash
Goulash

Reputation: 3838

Replacing a part of a line with bash / perl

I'm a noob at bash need to replace the mypassword part of this line in a file

"rpc-password": mypassword

with mynewpassword

I tried

perl -pi -e "s,PASSWORD,${password},g" "${user_conf}"

but it dosen't seem to do anything :( I can use anything that will work inside a bash script, it dosen't have to be bash or perl.

Upvotes: 5

Views: 9971

Answers (3)

TLP
TLP

Reputation: 67900

Using a loose regex without keeping backups is a bad idea. Especially if you intend to use dynamic replacement strings. While it may work just fine for something like "mypassword", it will break if someone tries to replace with the password "ass" with "butt":

"rpc-password": mypassword

Would become:

"rpc-pbuttword": butt

The more automation you seek, the more strict you need the regex to be, IMO.

I would anchor the replacement part to the particular configuration line that you seek:

s/^\s*"rpc-password":\s*\K\Q$mypassword\E\s*$/$mynewpassword/

No /g modifier, unless you intend to replace a password several times on the same line. \K will preserve the characters before it. Using \s* liberally will be a safeguard against user-edited configuration files where extra whitespace might have been added.

Also, importantly, you need to quote meta characters in the password. Otherwise a password such as t(foo)? Will also match a single t. In general, it will cause strange mismatches. This is why I added \Q...\E (see perldoc perlre) to the regex, which will allow variable interpolation, but escape meta characters.

Upvotes: 6

Bill
Bill

Reputation: 25555

You can also use sed for this:

sed -i 's/mypassword/mynewpassword/g' file

Upvotes: 1

ouah
ouah

Reputation: 145829

perl -pi -e 's/mypassword/mynewpassword/g' file

will work

Upvotes: 13

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