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Editorial Team
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Asked: 2026-05-19T17:43:45+00:00

Having some difficulty in replacing some single/double quoted text with sed and was wondering

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Having some difficulty in replacing some single/double quoted text with sed and was wondering what’s the correct method for these 2 examples

to change Memached.ini file contents from

[server]
server[] = "localhost:11211"

to 

[server]
server[] = "localhost:11211"
server[] = "localhost:11212"

and to change memcache.php file contents for these lines from

define('ADMIN_USERNAME','username');    // Admin Username
define('ADMIN_PASSWORD','password');    // Admin Password

$MEMCACHE_SERVERS[] = 'mymemcache-server1:11211'; // add more as an array
$MEMCACHE_SERVERS[] = 'mymemcache-server2:11211'; // add more as an array

to

define('ADMIN_USERNAME','myusername');  // Admin Username
define('ADMIN_PASSWORD','mypassword');      // Admin Password

$MEMCACHE_SERVERS[] = 'localhost:11211'; // add more as an array
$MEMCACHE_SERVERS[] = 'localhost:11212'; // add more as an array

I tried for example

sed -i 's/'ADMIN_USERNAME','memcache'/'ADMIN_USERNAME','u'/g' /var/www/html/memcache.php

while command runs, memcache.php file isn’t changed at all ?

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1 Answer

  1. Editorial Team

    You can replace the single quotes in the sed command with double-quoted single quotes. The shell sees a single quote as ending a string. So, let it. You had

    sed -i 's/'ADMIN_USERNAME','memcache'/'ADMIN_USERNAME','u'/g' /var/www/html/memcache.php

    But, if you replace the ‘ in the sed command with ‘”‘”‘, then shell will see the first ‘ as ending the first single-quoted string, then “‘” as a double-quoted single quote, and then the last ‘ as a beginning of a new single-quoted string. That’d be

    sed -i 's/'"'"'ADMIN_USERNAME'"'"','"'"'memcache'"'"'/'"'"'ADMIN_USERNAME'"'"','"'"'u'"'"'/g' /var/www/html/memcache.php

    You should also be able to do ‘\” in place of the ‘ within the command, for the same reason.

    sed -i 's/'\''ADMIN_USERNAME\'',\''memcache\''/\''ADMIN_USERNAME\'',\''u\''/g' /var/www/html/memcache.php

    But really, it’d be better to use an alternative mechanism. I’d suggest defining the source and target strings as variables, and then put those in the sed string.

    SRC="'ADMIN_USERNAME','memcache'"
DST="'ADMIN_USERNAME','u'"
sed -i "s/$SRC/$DST/g" /var/www/html/memcache.php

    That’s way more readable, and it makes it easier for you to handle the quoting mess in a sane way with bite-sized chunks. Yay “shell variable contents aren’t subject to word expansion unless you force it” knowledge. 🙂

    Make sure you don’t put a / in the $SRC or $DST variables, though. 😉

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