expansion with escape character

Question

I am having trouble doing expansion with this because of the escape character.

UNF\1122

Right now I am trying to stick with the really simple example of:

ps -ef | grep $USER

Eventually after I deal with the escape character I would like to do this.

ipcs -m | grep $USER | awk '{printf "%s ",$2}'

I know $USER has a value because I did this.

$ echo $USER UNF\1122

Please don't ask me why the administrator decided to put a \ in the username because I don't know.

To solve this I tried single quotes and double quotes. I have also tried to change username like this.

USER="UNF\\\\1122" and USER='UNF\\1122'

Answer 1

Tricky, as depending on the utility a \1 may have meaning, for example a back reference in grep, but not so in getent. Shell interpolation also complicates matters.

# getent sees a\\b, cannot find this literal string
$ getent passwd 'a\\b'

# let the shell interpolate \\ to \ so getent sees a\b
$ getent passwd a\\b
a\b:x:9999:9999:Slash Gordon:/:/bin/sh

# or no iterpolation, literal a\b passed to getent
$ getent passwd 'a\b'
a\b:x:9999:9999:Slash Gordon:/:/bin/sh

# oops, shell interpolated \\ to \ and thus grep sees \b metacharacter
$ grep "a\\b" /etc/passwd
vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
a\b:x:9999:9999:Slash Gordon:/:/bin/sh

# oops, also shell interpolation, so grep sees a\b metachar
$ grep a\\b /etc/passwd
vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
a\b:x:9999:9999:Slash Gordon:/:/bin/sh

# no interpolation, pass \\ to grep, which then treats as literal \
$ grep 'a\\b' /etc/passwd
a\b:x:9999:9999:Slash Gordon:/:/bin/sh
$