The following script reads from a file named "testonthis" line by line and then compares each line with a simple string, a string with special characters and a regular expression. If it doesn't match, then the script will print the line, otherwise not.
Space in Bash is so much important. So the following will work:
[ "$LINE" != "table_name" ]
But the following won't:
["$LINE" != "table_name"]
So please use as is:
cat testonthis | while read LINE
do
if [ "$LINE" != "table_name" ] && [ "$LINE" != "--------------------------------" ] && [[ "$LINE" =~ [^[:space:]] ]] && [[ "$LINE" != SQL* ]]; then
echo $LINE
fi
done
Bash 4+ examples. Note: not using quotes will cause issues when words contain spaces, etc. Always quote in Bash, IMO.
Here are some examples in Bash 4+:
Example 1, check for 'yes' in string (case insensitive):
if [[ "${str,,}" == *"yes"* ]] ;then
Example 2, check for 'yes' in string (case insensitive):
if [[ "$(echo "$str" | tr '[:upper:]' '[:lower:]')" == *"yes"* ]] ;then
Example 3, check for 'yes' in string (case sensitive):
if [[ "${str}" == *"yes"* ]] ;then
Example 4, check for 'yes' in string (case sensitive):
if [[ "${str}" =~ "yes" ]] ;then
Example 5, exact match (case sensitive):
if [[ "${str}" == "yes" ]] ;then
Example 6, exact match (case insensitive):
if [[ "${str,,}" == "yes" ]] ;then
Example 7, exact match:
if [ "$a" = "$b" ] ;then
Enjoy.
I did it in this way that is compatible with Bash and Dash (sh):
testOutput="my test"
pattern="my"
case $testOutput in (*"$pattern"*)
echo "if there is a match"
exit 1
;;
(*)
! echo there is no coincidence!
;;esac
I would probably use regexp matches if the input has only a few valid entries. E.g. only the "start" and "stop" are valid actions.
if [[ "${ACTION,,}" =~ ^(start|stop)$ ]]; then
echo "valid action"
fi
Note that I lowercase the variable $ACTION by using the double comma's. Also note that this won't work on too aged bash versions out there.
a="abc"
b="def"
# Equality Comparison
if [ "$a" == "$b" ]; then
echo "Strings match"
else
echo "Strings don't match"
fi
# Lexicographic (greater than, less than) comparison.
if [ "$a" \< "$b" ]; then
echo "$a is lexicographically smaller then $b"
elif [ "$a" \> "$b" ]; then
echo "$b is lexicographically smaller than $a"
else
echo "Strings are equal"
fi
Notes:
if and [ and ] are important> and < are redirection operators so escape it with \> and \< respectively for strings.To compare strings with wildcards use
if [[ "$stringA" == *$stringB* ]]; then
# Do something here
else
# Do Something here
fi
you can also use use case/esac
case "$string" in
"$pattern" ) echo "found";;
esac
I have to disagree one of the comments in one point:
[ "$x" == "valid" ] && echo "valid" || echo "invalid"
It's just it looks like one to, hmm, the uninitiated...
It uses common patterns as a language, in a way;
And after you learned the language.
It is a simple logical expression, with one special part: lazy evaluation of the logic operators.
[ "$x" == "valid" ] && echo "valid" || echo "invalid"
Each part is a logical expression; the first may be true or false, the other two are always true.
(
[ "$x" == "valid" ]
&&
echo "valid"
)
||
echo "invalid"
Now, when it is evaluated, the first is checked. If it is false, than the second operand of the logic and && after it is not relevant. The first is not true, so it can not be the first and the second be true, anyway.
Now, in this case is the the first side of the logic or || false, but it could be true if the other side - the third part - is true.
So the third part will be evaluated - mainly writing the message as a side effect. (It has the result 0 for true, which we do not use here)
The other cases are similar, but simpler - and - I promise! are - can be - easy to read!
(I don't have one, but I think being a UNIX veteran with grey beard helps a lot with this.)
Or, if you don't need else clause:
[ "$x" == "valid" ] && echo "x has the value 'valid'"
Source: Stackoverflow.com