How do I negate a test with regular expressions in a bash script

Question

Using GNU bash  version 4 0 35 1 -release  x86 64-suse-linux-gnu   I would like to negate a test with Regular Expressions  For example  I would like to conditionally add a path to the PATH variable  if the path is not already there  as in   TEMP  mnt silo bin if      PATH       TEMP       then PATH  PATH  else PATH  PATH  TEMP  fi TEMP  mnt silo Scripts  if      PATH       TEMP       then PATH  PATH  else PATH  PATH  TEMP  fi TEMP  mnt silo local bin if      PATH       TEMP       then PATH  PATH  else PATH  PATH  TEMP  fi export PATH   I m sure there are a million ways to do this  but what I would like to know is if the conditional can be negated somehow  as in  the erroneous    TEMP  mnt silo bin if       PATH       TEMP       then PATH  PATH  TEMP  fi TEMP  mnt silo Scripts  if       PATH       TEMP       then PATH  PATH  TEMP  fi TEMP  mnt silo local bin if       PATH       TEMP       then PATH  PATH  TEMP  fi export PATH

User · Answer

You can also put the exclamation mark inside the brackets:

if [[ ! $PATH =~ $temp ]]

but you should anchor your pattern to reduce false positives:

temp=/mnt/silo/bin
pattern="(^|:)${temp}(:|$)"
if [[ ! "${PATH}" =~ ${pattern} ]]

which looks for a match at the beginning or end with a colon before or after it (or both). I recommend using lowercase or mixed case variable names as a habit to reduce the chance of name collisions with shell variables.

User · Answer

Yes you can negate the test as SiegeX has already pointed out   However you shouldn t use regular expressions for this - it can fail if your path contains special characters  Try this instead         PATH          1          Source

User · Answer

You had it right  just put a space between the   and the    like if

User · Answer

I like to simplify the code without using conditional operators in such cases   TEMP  mnt silo bin      PATH       TEMP        PATH  PATH  TEMP

User · Answer

the safest way is to put the   for the regex negation within the       like this    if        STR     YOUR REGEX     then   otherwise it might fail on certain systems

[regex] How do I negate a test with regular expressions in a bash script?

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