I am new to Bash coding. I would like to concatenate a string to each element of a comma-separated strings "array".
This is an example of what I have in mind:
s=a,b,c
# Here a function to concatenate the string "_string" to each of them.
# Expected result:
a_string,b_string,c_string
One way:
$ s=a,b,c
$ echo ${s//,/_string,}_string
a_string,b_string,c_string
Using a proper array is generally a much more robust solution. It allows the values to contain literal commas, whitespace, etc.
s=(a b c)
printf '%s\n' "${s[#]/%/_string}"
As suggested by chepner, you can use IFS="," to merge the result with commas.
(IFS=","; echo "${s[#]/%/_string}")
(The subshell is useful to keep the scope of the IFS reassignment from leaking to the current shell.)
Simply, you could use a for loop
main() {
local input='a,b,c'
local append='_string'
# create an 'output' variable that is empty
local output=
# convert the input into an array called 'items' (without the commas)
IFS=',' read -ra items <<< "$input"
# loop over each item in the array, and append whatever string we want, in this case, '_string'
for item in "${items[#]}"; do
output+="${item}${append},"
done
# in the loop, the comma was re-added back. now, we must remove the so there are only commas _in between_ elements
output=${output%,}
echo "$output"
}
main
I've split it up in three steps:
Make it into an actual array.
Append _string to each element in the array using Parameter expansion.
Turn it back into a scalar (for which I've made a function called turn_array_into_scalar).
#!/bin/bash
function turn_array_into_scalar() {
local -n arr=$1 # -n makes `arr` a reference the array `s`
local IFS=$2 # set the field separator to ,
arr="${arr[*]}" # "join" over IFS and assign it back to `arr`
}
s=a,b,c
# make it into an array by turning , into newline and reading into `s`
readarray -t s < <(tr , '\n' <<< "$s")
# append _string to each string in the array by using parameter expansion
s=( "${s[#]/%/_string}" )
# use the function to make it into a scalar again and join over ,
turn_array_into_scalar s ,
echo "$s"
Related
I have a variable ($OUTPUT) that contains the following name / value pairs:
member_id=4611686018429783292
platform=Xbox
platform_id=1
character_id=2305843009264966985
period_dt=2020-11-25 20:31:14.923158 UTC
mode=all Crucible modes
mode_id=5
activities_entered=18
activities_won=10
activities_lost=8
assists=103
kills=233
average_kill_distance=15.729613
total_kill_distance=3665
seconds_played=8535
deaths=118
average_lifespan=71.72269
total_lifespan=8463.277
opponents_defeated=336
efficiency=2.8474576
kills_deaths_ratio=1.9745762
kills_deaths_assists=2.411017
suicides=1
precision_kills=76
best_single_game_kills=-1
Each line ends with \n.
I want to loop through them, and parse them into an associative array, and the access the values in the array by the variable names:
while read line
do
key=${line%%=*}
value=${line#*=}
echo $key=$value
data[$key]="$value"
done < <(echo "$OUTPUT")
#this always prints the last value
echo ${data['seconds_played']}
This seems to work, i.e. key/value print the right values, but when I try to pull any values from the array, it always returns the last value (in this case -1).
I feel like im missing something obvious, but have been banging my head against it for a couple of hours.
UPDATE: My particular issue is I'm running a version of bash (3.2.57 on OSX) that doesn't support associative arrays). I'll mark the correct answer below.
Without declare -A data, then data is a normal array. In normal arrays expressions in [here] first undergo expansions, then arithmetic expansion. Inside arithmetic expansion unset variables are expanded to 0. You are effectively only just setting data[0]=something, because data[$key] is data[seconds_played] -> variable seconds_played is not defined, so it expands to data[0]
Add declare -A data and it "should work". You could also just:
declare -A data
while IFS== read -r key value; do
data["$key"]="$value"
done <<<"$OUTPUT"
Try declaring data as an associative array before populating it, eg:
$ typeset -A data # declare as an associative array
$ while read line
do
key=${line%%=*}
value=${line#*=}
echo $key=$value
data[$key]="$value"
done <<< "${OUTPUT}"
$ typeset -p data
declare -A data=([mode]="all Crucible modes" [period_dt]="2020-11-25 20:31:14.923158 UTC" [deaths]="118" [best_single_game_kills]="-1" [efficiency]="2.8474576" [precision_kills]="76" [activities_entered]="18" [seconds_played]="8535" [total_lifespan]="8463.277" [average_lifespan]="71.72269" [character_id]="2305843009264966985" [kills]="233" [activities_won]="10" [average_kill_distance]="15.729613" [activities_lost]="8" [mode_id]="5" [assists]="103" [suicides]="1" [total_kill_distance]="3665" [platform]="Xbox" [kills_deaths_ratio]="1.9745762" [platform_id]="1" [kills_deaths_assists]="2.411017" [opponents_defeated]="336" [member_id]="4611686018429783292" )
$ echo "${data['seconds_played']}"
8535
I have a some file names in bash that I have acquired with
$ ones=$(find SRR*pass*1*.fq)
$ echo $ones
SRR6301033_pass_1_trimmed.fq
SRR6301034_pass_1_trimmed.fq
SRR6301037_pass_1_trimmed.fq
...
I then converted into an array so I can iterate over this list and perform some operations with filenames:
# convert to array
$ ones=(${ones// / })
and the iteration:
for i in $ones;
do
fle=$(basename $i)
out=$(echo $fle | grep -Po '(SRR\d*)')
echo "quants/$out.quant"
done
which produces:
quants/SRR6301033
SRR6301034
...
...
SRR6301220
SRR6301221.quant
However I want this:
quants/SRR6301033.quant
quants/SRR6301034.quant
...
...
quants/SRR6301220.quant
quants/SRR6301221.quant
Could somebody explain why what I'm doing doesn't work and how to correct it?
Why do you want this be done this complicated? You can get rid of all the unnecessary roundabouts and just use a for loop and built-in parameter expansion techniques to get this done.
# Initialize an empty indexed array
array=()
# Start a loop over files ending with '.fq' and if there are no such files
# the *.fq would be un-expanded and checking it against '-f' would fail and
# in-turn would cause the loop to break out
for file in *.fq; do
[ -f "$file" ] || continue
# Get the part of filename after the last '/' ( same as basename )
bName="${file##*/}"
# Remove the part after '.' (removing extension)
woExt="${bName%%.*}"
# In the resulting string, remove the part after first '_'
onlyFir="${woExt%%_*}"
# Append the result to the array, prefixing/suffixing strings 'quant'
array+=( quants/"$onlyFir".quant )
done
Now print the array to see the result
for entry in "${array[#]}"; do
printf '%s\n' "$entry"
done
Ways your attempt could fail
With ones=$(find SRR*pass*1*.fq) you are storing the results in a variable and not in an array. A variable has no way to distinguish if the contents are a list or a single string separated by spaces
With echo $ones i.e. an unquoted expansion, the string content is subject to word splitting. You might not see a difference as long as you have filenames with spaces, having one might let you interpret parts of the filename as different files
The part ${ones// / } makes no-sense in converting the string to an array as the attempt to use an unquoted variable $ones itself would be erroneous
for i in $ones; would be error prone for the said reasons above, the filenames with spaces could be interpreted as separated files instead of one.
I need to store a string that may include special characters (to be exact: *) into an array as individual strings. The string is returned by a function so at the point of the array declaration I do not know its contents
foo(){
in="my * string"
echo "$in"
}
arr=($(foo))
What I've already tried was:
arr=("$(foo)")
where * doesn't get expanded but the array consists of 1 string, and:
arr=($(foo | sed -r "s/[\*]/'*'/g"))
that replaces each occurence of * with the string: *. Which is not what I want to achieve. What I aim for is just storing each * from the returned string as *.
Storing an array this way does not expand the "*"
ins="my * string"
read -r -a array <<< "$ins"
echo "${array[*]}"
Short answer:
read -a arr <<< "$(foo)"
To elaborate -
Your function is correctly returning the single string "my * string".
Your assignment to an array executes the function in unquoted context, so the asterisk is evaluated and parsed to the names of everything in the directory.
Putting quotes around the outer parens makes the whole assignment into the string "(my * string)" - also not what you want. You need something that preserves the asterisk unexpanded into directory contents but parses the elements of the string into separate items in your array, yes?
read -a arr <<< "$(foo)"
This passes back the string properly quoted, and then reads it into the array after splitting with $IFS, so each item becomes an unexpanded string in the array.
$: echo "${#arr[#]}"
3
$: printf "%s\n" "${arr[#]}"
my
*
string
I'm trying to get back an array from perl to bash.
My perl scrip has an array and then I use return(#arr)
from my bash script I use
VAR = `perl....
when I echo VAR
I get the aray as 1 long string with all the array vars connected with no spaces.
Thanks
In the shell (and in Perl), backticks (``) capture the output of a command. However, Perl's return is normally for returning variables from subroutines - it does not produce output, so you probably want print instead. Also, in bash, array variables are declared with parentheses. So this works for me:
$ ARRAY=(`perl -wMstrict -le 'my #array = qw/foo bar baz/; print "#array"'`); \
echo "<${ARRAY[*]}> 0=${ARRAY[0]} 1=${ARRAY[1]} 2=${ARRAY[2]}"
<foo bar baz> 0=foo 1=bar 2=baz
In Perl, interpolating an array into a string (like "#array") will join the array with the special variable $" in between elements; that variable defaults to a single space. If you simply print #array, then the array elements will be joined by the variable $,, which is undef by default, meaning no space between the elements. This probably explains the behavior you mentioned ("the array vars connected with no spaces").
Note that the above will not work the way you expect if the elements of the array contain whitespace, because bash will split them into separate array elements. If your array does contain whitespace, then please provide an MCVE with sample data so we can perhaps make an alternative suggestion of how to return that back to bash. For example:
( # subshell so IFS is only affected locally
IFS=$'\n'
ARRAY=(`perl -wMstrict -e 'my #array = ("foo","bar","quz baz"); print join "\n", #array'`)
echo "0=<${ARRAY[0]}> 1=<${ARRAY[1]}> 2=<${ARRAY[2]}>"
)
Outputs: 0=<foo> 1=<bar> 2=<quz baz>
Here is one way using Bash word splitting, it will split the string on white space into the new array array:
array_str=$(perl -E '#a = 1..5; say "#a"')
array=( $array_str )
for item in ${array[#]} ; do
echo ": $item"
done
Output:
: 1
: 2
: 3
: 4
: 5
I'm having a input like that
field = <0xaaa 0xbbb>;
and would like to extract the two hex values so they can be used in a Makefile.
How would I go about that?
You can remove everything surrounding the two values with:
sed 's/.*<\(.*\)>.*/\1/'
Test:
% echo 'field = <0xaaa 0xbbb>;' | sed 's/.*<\(.*\)>.*/\1/'
0xaaa 0xbbb
If you need to dereference the values to variables:
declare -a values=($(sed 's/.*<\(.*\)>.*/\1/' input_file))
echo "${values[0]}" # 0xaaa
echo "${values[1]}" # 0xbbb
# ... If there are more lines in input_file then the array will be bigger ...
# ${values[2]} will contain next lValue
# ${values[3]} will contain next rValue
# ... and so on ...