Can someone explain why this simple bash script:
#!/bin/bash
myvar="Hello"
if [[ -z "$myvar" ]]; then
# echo "It's an unfilled string"
else
echo "It's a filled string!"
fi
gives me the error
./testscript: line 7: syntax error near unexpected token `else'
./testscript: line 7: `else'
However, if I remove the comment on the echo line, the script runs fine. Obviously, there is an issue with having commented lines within empty if statements. This this in mind, how do I fix it so I can have an empty if statement with comments?
There are no statements between then and else, so this is a syntax error. If you really want to do nothing in the if branch, then you can use a : (or true) as a placeholder:
#!/bin/bash
myvar="Hello"
if [[ -z "$myvar" ]]; then
# echo "It's an unfilled string"
:
else
echo "It's a filled string!"
fi
Better yet, reverse your logic:
#!/bin/bash
myvar="Hello"
if [[ -n "$myvar" ]]; then
echo "It's a filled string!"
fi
This is the way not to use if else statement.
#!/bin/bash
myvar="Hello"
[[ -n "$myvar" ]] && echo "It's a filled string!"
Also you can use this.
#!/bin/bash
myvar="Hello"
[[ -z "$myvar" ]] || echo "It's a filled string!"
Related
read answer #this will read what the user is typing in and makes a string for it
if [[ -z {answer} ]]
then
echo "Sorry that is not a valid choice, please select from the above list provided" #this will help pick up if the user just enters a blank option
if [[ $1{answer} ]]
then
echo "this has worked" #no clue if this will work going to try this and see if it works
if [[ $2{answer} ]]
then
echo "this is answer 2"
if [[ $3{answer} ]]
then
echo "this is answer 3"
if [[ $4{answer} ]]
then
echo "This is answer 4"
if [[ $Q{answer} ]]
then
echo "this is the quit button"
else
echo "no valid choice has been made"
fi
fi
fi
fi
fi
fi
so i am trying to run this code, i have closing arguments for each if statement, but every time i try and run it it shows "line 51: syntax error: unexpected end of file" the code goes up to line 50, i tried putting in ;; but it ran a syntax error on them, i tried converting with the dos2unix command but nothing, is there something i am missing?
Add the $ to this line, like so
if [[ -z ${answer} ]]
I am trying to read a parameter file in a shell script and would want to skip the lines which start with "#". Have been trying it on Ubuntu VM (default bash) and for something that I can't understand, it doesn't seem to work.
Following is the pseudo-code that I am using:
while read line
do
if [ grep -q "#" <<< "$line" ]; then
## Do nothing (Commented Out)
echo "$line Line is Commented out"
elif [ "$line" = "" ]; then
## Do nothing (Blank Line)
echo "Blank line"
else
#echo "read line is $line"
...some logic here
fi
done <input_file.ini
This yields the the following error: Syntax error: redirection unexpected
The if [[ $line == *#* ]] construct doesn't seem to work. My earlier experience was on AIX where everything worked fine.
Could someone guide me what I am doing wrong here?
PS: On a related note, how do I handle cases where I don't want to do anything? e.g. when there is no '#' character in the read line, I don't want to do anything. I can't leave my if block blank so I am just using echo 'some random' text. My task works good but just wanted to understand what's a good practice to handle this.
Your code is clearly running with /bin/sh, not bash.
An alternative to [[ $line = *"#"* ]] that works with /bin/sh is case.
Thus, the following will work with /bin/sh, or when invoked with sh yourscript:
#!/bin/sh
while read -r line; do : line="$line"
case $line in
*"#"*) echo "Line is commented out: $line";;
"") echo "Line is empty" ;;
*) key=${line%%=*}
value=${line#*=}
eval "$key="'$line' # unsafe, but works with /bin/sh, which doesn't have better
# indirect assignment approaches.
printf '%s\t\t-\t\t%s\n' "$key" "$value"
;;
esac
done <input_file.ini
Alternately, consider putting in a guard to handle the case when your script is invoked with a non-bash shell:
#!/bin/bash
case $BASH_VERSION in
'')
echo "ERROR: Run with a non-bash shell" >&2
if [ "$tried_reexec" ]; then
echo "ERROR: Already attempted reexec and failed" >&2
exit 1
fi
if [ -s "$0" ]; then
export tried_reexec=1
exec bash "$0" "$#"
fi
;;
esac
while read -r line; do
if [[ $line = *"#"* ]]; then
echo "Line is Commented out: $line"
elif [[ "$line" = "" ]]; then
echo "Blank line"
else
key=${line%%=*}; value=${line#*=}
printf -v "$key" %s "$value"
printf '%s\t\t-\t\t%s\n' "$key" "$value"
fi
done <input_file.ini
I really wasn't able to figure out the exact problem with double [[ ]] and the character search in a string. Thanks to everyone who tried to help me out. However this was acting as a deterrent and I didn't want to continue to fiddle for too long, I used a slightly different approach to handle my situation.
The following code works for me now:
while read line
do
first_char=`echo $line | cut -c 1`
if [ "$first_char" = "#" ]; then
: "do nothing here. Line is commented out"
elif [ "$line" = "" ]; then
: "do nothing here. Blank line"
else
KEY="$(echo $line | cut -d '=' -f1)"
VALUE="$(echo $line | cut -d '=' -f2)"
printf \v "$KEY" %s "$VALUE"
echo "$KEY\t\t-\t\t$VALUE"
fi
done < ${SCHEDULER_LOC}/inputs/script_params.ini
Also I was able to learn few things so incorporated them as well. I did get few negative scores for this question. Understandably so since this might be rudimentary for the experts but it was a genuine problem I was seeking some guidance on. Still, I am thankful that I learnt something new. Kudos to the community.
I am using shell to simple String regex match. Here is my shell
#!/bin/sh
MSG="ANK"
PATTERN="([A-Z]{3,5}[-][0-9]{2,5})"
if [ "$MSG" =~ "$PATTERN" ]; then
echo "MATCHED";
else
echo "not";
fi
It is giving error
abc.sh: 6: [: ANK: unexpected operator
How should I fix this?
Making the changes proposed by several contributors in the comments yields:
#!/bin/bash
MSG="ANK"
PATTERN="([A-Z]{3,5}[-][0-9]{2,5})"
if [[ "$MSG" =~ $PATTERN ]]; then
echo "MATCHED";
else
echo "not";
fi
Note the change to bash, the change to [[ and removal of the quotation marks around $PATTERN.
I want an if/then statement in Bash and I can't seem to get it to work. I would like to say "If the line begins with > character, then do this, else do something else".
I have:
while IFS= read -r line
do
if [[$line == ">"*]]
then
echo $line'first'
else
echo $line'second'
fi
done
But it isn't working.
I also tried to escape the ">" by saying:
if [[$line == ^\>*]]
Which didn't work either.
Both ways I am getting this error:
line 27: [[>blah: command not found
Suggestions?
Spaces are needed inside [[ and ]] as follows:
if [[ "$line" == ">"* ]]; then
echo "found"
else
echo "not found"
fi
This attempt attempt uses a regex:
line="> line"
if [[ $line =~ ^\> ]] ; then
echo "found"
else
echo "not found"
fi
This one uses a glob pattern:
line="> line"
if [[ $line == \>* ]] ; then
echo "found"
else
echo "not found"
fi
Spacing is important.
$ [[ ">test" == ">"* ]]; echo $?
0
$ [[ "test" == ">"* ]]; echo $?
1
if grep -q '>' <<<$line; then
..
else
..
fi
using grep is much better :)
I need to go through my ini file and check if the line begins with a bracket, to figure out that the new config has started. Is there a way of checking this in bash? I tried
line="[test]"
if [[ "$line" =~ [.* ]]; then
echo "Got it!"
else
echo "Nothing found"
fi
but it doesn't work for me. I presume that the bracket needs to be somehow escaped, but I can't find any info as to how. Any help will be much appreciated.
To do this, you should backslash the special character [, so :
line='[test]'
if [[ $line =~ ^\[ ]]; then
echo "Got it!"
else
echo "Nothing found"
fi
EXPLANATIONS
[ is the starting character to opening a REGEX class, like [0-9]
quotes are needed everywhere but not inside bash [[ ]] tests
It's terrible to use a regexp for that! please use a bash glob instead:
if [[ $line = [* ]]; then
echo 'Got it!'
else
echo "Nothing found"
fi
Hope this helps use bash more efficiently.