This is how my input string looks like:
INPUT_STRING="{/p1/p2=grabthistext}"
I want to print grabthistext from the INPUT_STRING.
I tried echo "${INPUT_STRING##*=}" which prints grabthistext}
How do I read only grabthistext using parameter expansion expression?
If you really want a single parameter expansion then you can use:
#!/bin/bash
shopt -s extglob
INPUT_STRING="{/p1/p2=grabthistext}"
echo "${INPUT_STRING//#(*=|\})}"
grabthistext
I would use a bash regex though:
#!/bin/bash
INPUT_STRING="{/p1/p2=grabthistext}"
[[ $INPUT_STRING =~ =(.*)} ]] && echo "${BASH_REMATCH[1]}"
grabthistext
temp="${INPUT_STRING##*=}"
echo "${temp%\}}"
grabthistext
You can do it in two steps: first extract the fragment after = as you already did, and store it in a new variable. Then use the same technique to remove the undesired } suffix:
INPUT_STRING="{/p1/p2=grabthistext}"
TEMP_STRING=${INPUT_STRING##*=}
OUTPUT_STRING=${TEMP_STRING%\}}
echo "$OUTPUT_STRING"
# grabthistext
Check it online.
Related
Here is my code
vmname="$1"
EXCEPTLIST="desktop-01|desktop-02|desktop-03|desktop-04"
if [[ $vmname != #(${EXCEPTLIST}) ]]; then
echo "${vmname}"
else
echo "Its in the exceptlist"
fi
The above code works perfectly but my question is , the EXCEPTLIST can be a long line, say 100 server names. In that case its hard to put all that names in one line. In that situation is there any way to make the variable EXCEPTLIST to be a multiline variable ? something like as follows:
EXCEPTLIST="desktop-01|desktop-02|desktop-03| \n
desktop-04|desktop-05|desktop-06| \n
desktop-07|desktop-08"
I am not sure but was thinking of possibilities.
Apparently I would like to know the terminology of using #(${})- Is this called variable expansion or what ? Does anyone know the documentation/explain to me about how this works in bash. ?
One can declare an array if the data/string is long/large. Use IFS and printf for the format string, something like:
#!/usr/bin/env bash
exceptlist=(
desktop-01
desktop-02
desktop-03
desktop-04
desktop-05
desktop-06
)
pattern=$(IFS='|'; printf '#(%s)' "${exceptlist[*]}")
[[ "$vmname" != $pattern ]] && echo good
In that situation is there any way to make the variable EXCEPTLIST to be a multiline variable ?
With your given input/data an array is also a best option, something like:
exceptlist=(
'desktop-01|desktop-02|desktop-03'
'desktop-04|desktop-05|desktop-06'
'desktop-07|desktop-08'
)
Check what is the value of $pattern variable one way is:
declare -p pattern
Output:
declare -- pattern="#(desktop-01|desktop-02|desktop-03|desktop-04|desktop-05|desktop-06)"
Need to test/check if $vmname is an empty string too, since it will always be true.
On a side note, don't use all upper case variables for purely internal purposes.
The $(...) is called Command Substitution.
See LESS=+'/\ *Command Substitution' man bash
In addition to what was mentioned in the comments about pattern matching
See LESS=+/'(pattern-list)' man bash
See LESS=+/' *\[\[ expression' man bash
s there any way to make the variable EXCEPTLIST to be a multiline variable ?
I see no reason to use matching. Use a bash array and just compare.
exceptlist=(
desktop-01
desktop-02
desktop-03
desktop-04
desktop-05
desktop-06
)
is_in_list() {
local i
for i in "${#:2}"; do
if [[ "$1" = "$i" ]]; then
return 0
fi
done
return 1
}
if is_in_list "$vmname" "${EXCEPTLIST[#]}"; then
echo "is in exception list ${vmname}"
fi
#(${})- Is this called variable expansion or what ? Does anyone know the documentation/explain to me about how this works in bash. ?
${var} is a variable expansion.
#(...) are just characters # ( ).
From man bash in Compund commands:
[[ expression ]]
When the == and != operators are used, the string to the right of the operator is considered a pattern and matched according to the rules
described below under Pattern Matching, as if the extglob shell option were enabled. ...
From Pattern Matching in man bash:
#(pattern-list)
Matches one of the given patterns
[[ command receives the #(a|b|c) string and then matches the arguments.
There is absolutely no need to use Bash specific regex or arrays and loop for a match, if using grep for raw string on word boundary.
The exception list can be multi-line, it will work as well:
#!/usr/bin/sh
exceptlist='
desktop-01|desktop-02|desktop-03|
deskop-04|desktop-05|desktop-06|
desktop-07|deskop-08'
if printf %s "$exceptlist" | grep -qwF "$1"; then
printf '%s is in the exceptlist\n' "$1"
fi
I wouldn't bother with multiple lines of text. This is would be just fine:
EXCEPTLIST='desktop-01|desktop-02|desktop-03|'
EXCEPTLIST+='desktop-04|desktop-05|desktop-06|'
EXCEPTLIST+='desktop-07|desktop-08'
The #(...) construct is called extended globbing pattern and what it does is an extension of what you probably already know -- wildcards:
VAR='foobar'
if [[ "$VAR" == fo?b* ]]; then
echo "Yes!"
else
echo "No!"
fi
A quick walkthrough on extended globbing examples: https://www.linuxjournal.com/content/bash-extended-globbing
#!/bin/bash
set +o posix
shopt -s extglob
vmname=$1
EXCEPTLIST=(
desktop-01 desktop-02 desktop-03
...
)
if IFS='|' eval '[[ ${vmname} == #(${EXCEPTLIST[*]}) ]]'; then
...
Here's one way to load a multiline string into a variable:
fn() {
cat <<EOF
desktop-01|desktop-02|desktop-03|
desktop-04|desktop-05|desktop-06|
desktop-07|desktop-08
EOF
}
exceptlist="$(fn)"
echo $exceptlist
As to solving your specific problem, I can think of a variety of approaches.
Solution 1, since all the desktop has the same desktop-0 prefix and only differ in the last letter, we can make use of {,} or {..} expansion as follows:
vmname="$1"
found=0
for d in desktop-{01..08}
do
if [[ "$vmname" == $d ]]; then
echo "It's in the exceptlist"
found=1
break
fi
done
if (( !found )); then
echo "Not found"
fi
Solution 2, sometimes, it is good to provide a list in a maintainable clear text list. We can use a while loop and iterate through the list
vmname="$1"
found=0
while IFS= read -r d
do
if [[ "$vmname" == $d ]]; then
echo "It's in the exceptlist"
found=1
break
fi
done <<EOF
desktop-01
desktop-02
desktop-03
desktop-04
desktop-05
desktop-06
desktop-07
desktop-08
EOF
if (( !found )); then
echo "Not found"
fi
Solution 3, we can desktop the servers using regular expressions:
vmname="$1"
if [[ "$vmname" =~ ^desktop-0[1-8]$ ]]; then
echo "It's in the exceptlist"
else
echo "Not found"
fi
Solution 4, we populate an array, then iterate through an array:
vmname="$1"
exceptlist=()
exceptlist+=(desktop-01 desktop-02 desktop-03 deskop-04)
exceptlist+=(desktop-05 desktop-06 desktop-07 deskop-08)
found=0
for d in ${exceptlist[#]}
do
if [[ "$vmname" == "$d" ]]; then
echo "It's in the exceptlist"
found=1
break;
fi
done
if (( !found )); then
echo "Not found"
fi
The initial string is RU="903B/100ms"
from which I wish to obtain B/100ms.
Currently, I have written:
#!/bin/bash
RU="903B/100ms"
RU=${RU#*[^0-9]}
echo $RU
which returns /100ms since the parameter expansion removes up to and including the first non-numeric character. I would like to keep the first non-numeric character in this case. How would I do this by amending the above text?
You can use BASH_REMATCH to extract the desired matching value:
$ RU="903B/100ms"
$ [[ $RU =~ ^([[:digit:]]+)(.*) ]] && echo ${BASH_REMATCH[2]}
B/100ms
Or just catch the desired part as:
$ [[ $RU =~ ^[[:digit:]]+(.*) ]] && echo ${BASH_REMATCH[1]}
B/100ms
Assuming shopt -s extglob:
RU="${RU##+([0-9])}"
echo "903B/100ms" | sed 's/^[0-9]*//g'
B/100ms
I want to compare Hello World to hello world. The result should be true, as if they were equal. I'm doing:
while read line; do
newLine="$newLine$line"
done < $1
newp="Hello World"
if (( ${newp,,}==${newLine,,} )); then
echo "true"
else
echo "false"
fi
when I pass a text file consisting of:
#filename: file.txt
hello world
The output seems to be:
./testScript.txt: line 20: 0à»: hello world==hello world : syntax error in expression (error token is "world==hello world ")
+ echo false
What am I doing wrong here? Also, a bit unrelated, is there any way to pass the line that is in file.txt to a string(newLine) without doing that while I have done?
You should add commas and change the double parentheses to single brackets. The if statement should be something like:
if [ "${newp,,}" = "${newLine,,}" ]; then
And in relation to that while loop... It depends on what you want to do. If, like in this case, you want to get the entire file and save it as a single string, you could simply do:
line=$(cat $1)
I would suggest you only use that loop you wrote if you are trying to parse the file line by line, i.e. adding if statements, using different variables and so on. But for a simple case like this one, cat will do just fine.
There is a shell option, nocasematch, that enables case insensitive pattern matching for use with [[ and case.
Comparing strings that differ by casing only:
$ var1=lowercase
$ var2=LOWERCASE
$ [[ $var1 == $var2 ]] && echo "Matches!" || echo "Doesn't match!"
Doesn't match!
Now enabling the shell option and trying again:
$ shopt -s nocasematch
$ [[ $var1 == $var2 ]] && echo "Matches!" || echo "Doesn't match!"
Matches!
Just make sure to turn it off again with shopt -u nocasematch if you don't want to do all comparisons case insensitive.
I have the following string
git#bitbucket.org:user/my-repo-name.git
I want to extract this part
my-repo-name
With bash:
s='git#bitbucket.org:user/my-repo-name.git'
[[ $s =~ ^.*/(.*)\.git$ ]]
echo ${BASH_REMATCH[1]}
Output:
my-repo-name
Another method, using bash's variable substitution:
s='git#bitbucket.org:user/my-repo-name.git'
s1=${s#*/}
echo ${s1%.git}
Output:
my-repo-name
I'm not sure if there's a way to combine the # and % operators into a single substitution.
I'd like to get the length of the string that I get when i use "$*" in my function.
I tried:
echo ${#"$*"}
and
echo ${#"*"}
both gave me a bad substitution error.
I don't think you can do it in a single command. However, this seems to work:
#!/bin/bash
a="$#"
echo "${#a}"
Using a temporary variable is the only one basic way, and you need to unset IFS or set it to empty string to prevent spaces in between. And use $* not $# for it would give you spaces in between:
IFS= eval "__=\"\$*\""
echo "${#__}"
Another way is to loop through all strings:
L=0; for __; do (( L += ${#__} )); done
echo "$L"
You can use one of the following.
expr length "$*"
echo "$*" | awk '{print length}'
$# holds the number of positional parameters passed to the function.
Try it:
#!/bin/bash
t() {
echo "num args=$#"
echo "all $*"
}
t "$#"