Linux Check if string exists as separate word (not as substring of another)

Question

I have a file that contains strings, and I would like to check if a string exists in that file as a separate word. example:

string = rambox

• file that contains "rambox":

  initrd=yahya/rambox/initramfs11.cpio.gz rambox ramdisk_size=5242880 ...

"grep" command will tell that "rambox" exists

• file not containing "rambox"

  initrd=yahya/rambox/initramfs11.cpio.gz ramdisk_size=5242880 ...

"grep" command will tell that "rambox" exists coz it exists as a substring of the path "initrd=yahya/rambox/initramfs11.cpio.gz" and this is not correct. I want to obtain that "rambox" doesn't exist in the second example. Is there a way ?

Answer 1

You can use grep with the -P flag:

grep -P '^rambox | rambox$| rambox '

Or even better:

grep -P '(^| )rambox($| )'

• ^ matches beginning of line
• $ matches end of line
• | is OR regex
• -P, --perl-regexp PATTERN is a Perl regular expression

Answer 2

Sounds like you want "rambox" to be surrounded by any amount of white-space or at the beginning or ending of the line. \\b and other word boundary solutions (eg, grep -w ) won't work here, because / counts as a non-word.

You could write your own interpretation of "word boundary" , but in this simple case it's not really worth it.

For this case, I'd probably just manually handle the beginning of line and end of line scenarios:

$ cat -vet junk
rambox$
 rambox$
rambox $
 rambox$
 foo rambox bar$
 foo  rambox bar$
/rambox/$
ramboxfoo$
ramboxfoo $
 foorambox$
 foorambox $

$ egrep '(^\s*rambox\s+|\s+rambox\s+|\s+rambox\s*$)' junk
 rambox
rambox
 rambox
 foo rambox bar
 foo  rambox bar

Answer 3

even the answer from Maroun Maroun sims right I would change space by this regexp [[:space:]] which will cover all free space like for example tab

input file

# cat testfile
rambox test test
testrambox test test
test test rambox        with tab
test test rambox
test testrambox
#

output:

# grep -P '(^|[[:space:]])rambox($|[[:space:]])' testfile
rambox test test
test test rambox        with tab
test test rambox
#