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Why should there be spaces around '[' and ']' in Bash?
(5 answers)
Closed 4 years ago.
I am trying to run simple code block.
It gives error on fourth line as "syntax error near `$1'"
=~ means Matches Regular Expression
How should I use '$1' variable with this operator?
Here is my code:
if [[ $1 -gt 3 ]] && [[ $1 -lt 7 ]]
then
echo "$1 is between 3 and 7"
elif [[ $1 =~ "Jeff"]] || [[ $1 =~ "Roger" ]] || [[ $1 =~ "Brian" ]]
then
echo "$1 works in the Data Science Lab"
else
echo "You entered: $1, not what I was looking for.."
fi
Very funny indeed. You've typed the first condition in that line as [[ $1 =~ "Jeff"]], so without a space between "Jeff" and ]] bash interprets them as a single string, which is obviously not your pattern, and the whole parse fails and line structure crashes. If you add that space:
if [[ $1 =~ "Jeff" ]] || [[ $1 =~ "Roger" ]] || [[ $1 =~ "Brian" ]]
then it works... seemingly...
Related
I found this question for how to do conditional assignment in bash, but what I'm trying to do is a little more complex, and I can't seem to get the syntax right. The condition in my case is to test a variable to see if it exists, and the output is concatenated to a string.
Here's what I have so far:
fwversion="${BASH_REMATCH[1]}.$(( [[ BASH_REMATCH[2] ]] ? BASH_REMATCH[2] : 0 ))"
Which produces this error message:
bash: line 41: [[ BASH_REMATCH[2] ]] ? BASH_REMATCH[2] : 0 : syntax error:
operand expected (error token is "[[ BASH_REMATCH[2] ]] ? BASH_REMATCH[2] : 0 ")
Here's what I'm trying to achieve as C++ code:
std::string fwversion = BASH_REMATCH[1] + "." + ((BASH_REMATCH[2]) ? : BASH_REMATCH[2] : 0);
What's the correct syntax to do this in bash? Thanks.
Looks like [[ ... ]] are not understood in an arithmetic expression.
I'd do this:
fwversion=${BASH_REMATCH[1]}
[[ ${BASH_REMATCH[2]} ]] && fwversion+=${BASH_REMATCH[2]} || fwversion+=0
or
[[ ${BASH_REMATCH[2]} ]] && ext=${BASH_REMATCH[2]} || ext=0
fwversion="${BASH_REMATCH[1]}.$ext"
On second thought, I wouldn't do that at all, I'd use the power of the shell's parameter expansion
str="foo:bar"
if [[ $str =~ ^([a-z]+):([a-z]*)$ ]]; then
echo "${BASH_REMATCH[1]}.${BASH_REMATCH[2]:-0}"
fi
foo.bar
str="foo:"
if [[ $str =~ ^([a-z]+):([a-z]*)$ ]]; then
echo "${BASH_REMATCH[1]}.${BASH_REMATCH[2]:-0}"
fi
foo.0
I'm trying to write an if statement in bash that will exit if the variable supplied is not an integer. I will eventually be nesting this if statement within a while loop.
When I do run this I am getting an syntax error.
#!/bin/bash
if [ $f1 != ^[0-9]+$ ]
then
exit 1
fi
I have always like the integer test using the equality test construct:
[ $var -eq $var 2>/dev/null ] || exit 1
If var is not an integer, the equality fails due to the error generated. It is also POSIX compliant as it doesn't rely on character classes or the bash [[ construct.
You better negate the condition like this:
if [[ ! "$f1" =~ ^[0-9]+$ ]]; then
exit 1
fi
note the [[ and ]] syntax for the regular expressions, together with ! to negate it. Then, we use =~ for regexs.
Test
$ r=23a
$ [[ ! "$r" =~ ^[0-9]+$ ]] && echo "no digit" || echo "digit"
no digit
$ r=23
$ [[ ! "$r" =~ ^[0-9]+$ ]] && echo "no digit" || echo "digit"
digit
I have the following command in my script. It works fine with one exception; it also matches partial entries. I want the match to be exact.
a=mary jane uger dodo baba
b=mary
c=ma
if [[ "$a" =~ "$b" ]] && [ -n "$1" ]; then
echo it matches
else
echo it does not match
fi
So no matter if in the if statement i use value $b or $c they both match.
I want to ensure that the entry is fully match and not partially. So
this should work and give exact match.
if [[ "$a" =~ "$b" ]]
and this should not work partial match
if [[ "$a" =~ "$c" ]]
Can someone help please?
here is my exact code
if [[ "$a" =~ "$b" ]]; then
echo something
fi
Put a space or end anchor in in the end for regex comparison to make sure there is no partial word match:
a='mary jane uger dodo baba'
b='mary'
c='ma'
# will match
[[ "$a" =~ "$b"( |$) ]]
# won't match
[[ "$a" =~ "$c"( |$) ]]
z='\>'
[[ $a =~ $b$z ]] # true
[[ $a =~ $c$z ]] # false
does bash support word boundary regular expressions?
I'm trying to check if some string from length 1 and has only following chars: [RGWBO].
I'm trying the following but it doesn't work, what am I missing?
if [[ !(${line[4]} =~ [RGWBO]) ]];
This is what you want:
if [[ ${line[4]} =~ ^[RGWBO]+$ ]];
This means that the string right from the start till the end must have [RGWBO] characters one or more times.
If you want to negate the expression just use ! in front of [[ ]]:
if ! [[ ${line[4]} =~ ^[RGWBO]+$ ]];
Or
if [[ ! ${line[4]} =~ ^[RGWBO]+$ ]];
This one would work with any usable version of Bash:
[[ -n ${LINE[0]} && ${LINE[0]} != *[^RGWB0]* ]]
Even though I prefer the simplicity of extended globs:
shopt -s extglob
[[ ${LINE[0]} == +([RGWBO]) ]]
Use expr (expression evaluator) to do substring matching.
#!/bin/bash
pattern='[R|G|W|B|O]'
string=line[4]
res=`expr match "$string" $pattern`
if [ "${res}" -eq "1" ]; then
echo 'match'
else
echo 'doesnt match'
fi
Approach
Test the string length with ${#myString}, if it's egal to 1 proceed to step 2 ;
Does is contains your pattern.
Code
re='[RGWBO]';
while read -r line; do
if (( ${#line} == 1 )) && [[ $line == $re ]]; then
echo "yes: $line"
else
echo "no: $line"
fi
done < test.txt
Resources
You may want to look at the following links:
Bash: Split string into character array's answer ;
Length of a string, use ${#myString} ;
Extracting parts of strings, use ${myString:0:8} ;
Data
The test.txt file contains this
RGWBO
RGWB
RGW
RG
R
G
W
B
O
V
if [[ $line == *"option 1"* ]]
then
CURRENT_OPTION=1
fi
if [[ $line == *"option 2"* ]]
then
CURRENT_OPTION=2
fi
if [[ $line =~ "What i want" ]]
then
if [[ $CURRENT_OPTION -eq 1 ]]
then
MEM1=$(awk '/Used heap/ { gsub(/M/, " "); print $4 }')
elif [[ $CURRENT_OPTION -eq 2 ]]
then
MEM2=$(awk '/Used heap/ { gsub(/M/, " "); print $4 }')
fi
fi
Because CURRENT_OPTION is defined within an if, its value is not correct when checked in the third if. How do I pass it out so that it is?
Just declare CURRENT_OPTION at the top, something like:
declare -i CURRENT_OPTION=0
i to declare it as an int.
In all of your if statements you should enclose the variables in double quotes. If the variable is an empty string (or if the variable doesn't exist) then the if statement will not contain enough arguments and will throw an error.
Here is an example:
if [[ $var -eq 1 ]]
then
echo yes
else
echo no
fi
If var is uninitialised, bash will expand the statement to look like this:
if [[ -eq 1 ]]
then
echo yes
else
echo no
fi
There are not enough arguments to make the if statement valid here, and bash will throw an error:
bash: conditional binary operator expected
bash: syntax error near `1'
By wrapping the variable in quotes, this situation is avoided. This statement:
if [[ "$var" -eq 1 ]]
...
is expanded to:
if [[ "" -eq 1 ]]
...
and now the if statement has enough arguments (the first one being an empty string) to parse.