I am trying to parse a command in shell, and in one of the options I want to save in a variable if a string has "r", "w", "x", one of those, all of them, or a mix, but only these three. No other characters should be allowed!
I tried a case where:
$2 in *r*) ;; *w*) ;; *x*) ;; * ) echo no ;;
esac
But in this case if there is written zr it will pass, as it has an "r". I only want to make it pass as long as it has one of these three, the three of them, or two of them (any kind of combination), but no other characters.
In BASH you can use regex for this check like this:
re='^[rwx]+$'
s='rw'
[[ $s =~ $re ]] && echo "yes" || echo "no"
yes
s='zr'
[[ $s =~ $re ]] && echo "yes" || echo "no"
no
Regex ^[rwx]+$ will allow 1 or more of r or w or x letters.
With extended pattern matching in Bash (shopt -s extglob):
if [[ $var == +([rwx]) ]]; then
echo "Matches!"
else
echo "Does not match!"
fi
The +([rwx]) pattern is "one or more of r, w or x".
Related
How do I compare a variable to a string (and do something if they match)?
Using variables in if statements
if [ "$x" = "valid" ]; then
echo "x has the value 'valid'"
fi
If you want to do something when they don't match, replace = with !=. You can read more about string operations and arithmetic operations in their respective documentation.
Why do we use quotes around $x?
You want the quotes around $x, because if it is empty, your Bash script encounters a syntax error as seen below:
if [ = "valid" ]; then
Non-standard use of == operator
Note that Bash allows == to be used for equality with [, but this is not standard.
Use either the first case wherein the quotes around $x are optional:
if [[ "$x" == "valid" ]]; then
or use the second case:
if [ "$x" = "valid" ]; then
Or, if you don't need an else clause:
[ "$x" == "valid" ] && echo "x has the value 'valid'"
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 $a"
else
echo "Strings are equal"
fi
Notes:
Spaces between if and [ and ] are important
> and < are redirection operators so escape it with \> and \< respectively for strings.
To compare strings with wildcards, use:
if [[ "$stringA" == *"$stringB"* ]]; then
# Do something here
else
# Do something here
fi
I have to disagree one of the comments in one point:
[ "$x" == "valid" ] && echo "valid" || echo "invalid"
No, that is not a crazy oneliner
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.
Actually, it's nice to read
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.)
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 $LINE
fi
done
You can also use use case/esac:
case "$string" in
"$pattern" ) echo "found";;
esac
Bash 4+ examples. Note: not using quotes will cause issues when words contain spaces, etc. Always quote in Bash, IMO.
Here are some examples in Bash 4+:
Example 1, check for 'yes' in string (case insensitive):
if [[ "${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 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.
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 was struggling with the same situation for a while, here is how I could resolve:
if [ "$var1" == "$var2" ]; then
#dowhateveryouwant
fi
Be careful with the spaces left before and after the comparison sign, otherwise it won't work or it'll give you an unexpected result.
I've spent so much time on using a single equal(=) sign but didn't work. I Hope it can help.
Are you having comparison problems? (like below?)
var="true"
if [[ $var == "true" ]]; then
# It should be working, but it is not...
else
# It is falling here...
fi
Try like the =~ operator (regular expression operator) and it might work:
var="true"
if [[ $var =~ "true" ]];then
# Now it works here!!
else
# No more inequality
fi
Bash regex operator =~ (official reference)
StackOverflow further examples (here)
How do I compare a variable to a string (and do something if they match)?
Using variables in if statements
if [ "$x" = "valid" ]; then
echo "x has the value 'valid'"
fi
If you want to do something when they don't match, replace = with !=. You can read more about string operations and arithmetic operations in their respective documentation.
Why do we use quotes around $x?
You want the quotes around $x, because if it is empty, your Bash script encounters a syntax error as seen below:
if [ = "valid" ]; then
Non-standard use of == operator
Note that Bash allows == to be used for equality with [, but this is not standard.
Use either the first case wherein the quotes around $x are optional:
if [[ "$x" == "valid" ]]; then
or use the second case:
if [ "$x" = "valid" ]; then
Or, if you don't need an else clause:
[ "$x" == "valid" ] && echo "x has the value 'valid'"
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 $a"
else
echo "Strings are equal"
fi
Notes:
Spaces between if and [ and ] are important
> and < are redirection operators so escape it with \> and \< respectively for strings.
To compare strings with wildcards, use:
if [[ "$stringA" == *"$stringB"* ]]; then
# Do something here
else
# Do something here
fi
I have to disagree one of the comments in one point:
[ "$x" == "valid" ] && echo "valid" || echo "invalid"
No, that is not a crazy oneliner
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.
Actually, it's nice to read
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.)
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 $LINE
fi
done
You can also use use case/esac:
case "$string" in
"$pattern" ) echo "found";;
esac
Bash 4+ examples. Note: not using quotes will cause issues when words contain spaces, etc. Always quote in Bash, IMO.
Here are some examples in Bash 4+:
Example 1, check for 'yes' in string (case insensitive):
if [[ "${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 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.
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 was struggling with the same situation for a while, here is how I could resolve:
if [ "$var1" == "$var2" ]; then
#dowhateveryouwant
fi
Be careful with the spaces left before and after the comparison sign, otherwise it won't work or it'll give you an unexpected result.
I've spent so much time on using a single equal(=) sign but didn't work. I Hope it can help.
Are you having comparison problems? (like below?)
var="true"
if [[ $var == "true" ]]; then
# It should be working, but it is not...
else
# It is falling here...
fi
Try like the =~ operator (regular expression operator) and it might work:
var="true"
if [[ $var =~ "true" ]];then
# Now it works here!!
else
# No more inequality
fi
Bash regex operator =~ (official reference)
StackOverflow further examples (here)
How to check if a string contains version in numberic/decimal format in shell script
for eg we have 1.2.3.5 or 2.3.5
What if we do not have a constraint on the number of characters we have in here. It could x.x.x.x or x.x as well.
If you're using bash, you can use the =~ regex match binary operator, for example:
pax> if [[ 1.x20.3 =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]] ; then echo yes ; fi
pax> if [[ 1.20.3 =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]] ; then echo yes ; fi
yes
For your particular test data, the following regex will do the trick:
^[0-9]+(\.[0-9]+)*$
(a number followed by any quantity of .<number> extensions) although, if you want to handle edge cases like 1.2-rc7 or 4.5-special, you'll need something a little more complex.
Using bash regular expressions:
echo -n "Test: "
read i
if [[ $i =~ ^[0-9]+(\.[0-9]+){2,3}$ ]];
then
echo Yes
fi
This accepts digits.digits.digits or digits.digits.digits.digits
Change {2,3} to shrink or enlarge the acceptable number of .digits (or {2,} for "at least 2")
^ means beginning of string
[0-9]+ means at least one digit
\. is a dot
(...){2,3} accepts 2 or 3 of what's inside the ()
$ means end of string
And if you're truly restricted to the Bourne shell, then use expr:
if expr 1.2.3.4.5 : '^[0-9][.0-9]*[0-9]$' > /dev/null; then
echo "yep, it's a version number"
fi
I'm sure there are solutions involving awk or sed, but this will do.
Flip the logic: check if it contains an "invalid" character:
$ str=1.2.3.4.5; [[ $str == *[^0-9.]* ]] && echo nope || echo yup
yup
$ str=123x4.5; [[ $str == *[^0-9.]* ]] && echo nope || echo yup
nope
Downside to this answer:
$ str=123....; [[ $str == *[^0-9.]* ]] && echo nope || echo yup
yup
In a bash (version 3.2.48) script I get a string that can be something like:
'XY'
' Y'
'YY'
etc
So, I have either an alphabetic character OR a space (first slot), then the relevant character (second slot). I tried some variation (without grep, sed, ...) like:
if [[ $string =~ ([[:space]]{1}|[[:alpha:]]{1})M ]]; then
and
if [[ $string =~ (\s{1}|.{1})M ]]; then
but my solutions did not always work correctly (matching correctly every combination).
This should work for you:
if [[ $string =~ [[:space:][:alpha:]]M ]]; then
if [[ ${string:1:1} == "M" ]]; then
echo Heureka
fi
or (if you want to do it with patterns)
if [[ $string =~ ([[:space:]]|[[:alpha:]])M ]]; then
echo Heureka
fi
or (even simpler)
if [[ $string == ?M ]]; then
echo Heureka
fi
Without using regular expressions, simply pattern matching is sufficient:
if [[ $string == [[::upper:]\ ]M ]]; then
echo match
fi
Given your example, you want [[:upper:]] rather than merely [[:alpha:]]
I am doing some bash script and now I got one variable call source and one array called samples, like this:
source='country'
samples=(US Canada Mexico...)
as I want to expand the number of sources (and each source has its own samples) I tried to add some arguments to do this. I tried this:
source=""
samples=("")
if [ $1="country" ]; then
source="country"
samples="US Canada Mexico..."
else
echo "try again"
fi
but when I ran my script source countries.sh country it didn't work.
What am I doing wrong?
Don't forget about spaces:
source=""
samples=("")
if [ $1 = "country" ]; then
source="country"
samples="US Canada Mexico..."
else
echo "try again"
fi
You can use either "=" or "==" operators for string comparison in bash. The important factor is the spacing within the brackets. The proper method is for brackets to contain spacing within, and operators to contain spacing around. In some instances different combinations work; however, the following is intended to be a universal example.
if [ "$1" == "something" ]; then ## GOOD
if [ "$1" = "something" ]; then ## GOOD
if [ "$1"="something" ]; then ## BAD (operator spacing)
if ["$1" == "something"]; then ## BAD (bracket spacing)
Also, note double brackets are handled slightly differently compared to single brackets ...
if [[ $a == z* ]]; then # True if $a starts with a "z" (pattern matching).
if [[ $a == "z*" ]]; then # True if $a is equal to z* (literal matching).
if [ $a == z* ]; then # File globbing and word splitting take place.
if [ "$a" == "z*" ]; then # True if $a is equal to z* (literal matching).
It seems that you are looking to parse commandline arguments into your bash script. I have searched for this recently myself. I came across the following which I think will assist you in parsing the arguments:
http://rsalveti.wordpress.com/2007/04/03/bash-parsing-arguments-with-getopts/
I added the snippet below as a tl;dr
#using : after a switch variable means it requires some input (ie, t: requires something after t to validate while h requires nothing.
while getopts “ht:r:p:v” OPTION
do
case $OPTION in
h)
usage
exit 1
;;
t)
TEST=$OPTARG
;;
r)
SERVER=$OPTARG
;;
p)
PASSWD=$OPTARG
;;
v)
VERBOSE=1
;;
?)
usage
exit
;;
esac
done
if [[ -z $TEST ]] || [[ -z $SERVER ]] || [[ -z $PASSWD ]]
then
usage
exit 1
fi
./script.sh -t test -r server -p password -v