Extract specific substring in shell - shell

Question

I have a file which contains following line:
ro fstype=sd timeout=10 console=ttymxc1,115200 show=true
I'd like to extract and store fstype attribue "sd" in a variable.
I did the job using bash
IFS=" " read -a args <<< file
for arg in ${args[#]}; do
if [[ "$arg" =~ "fstype" ]]; then
id=$(cut -d "=" -f2 <<< "$arg")
echo $id
fi
done
and following awk command in another shell script:
awk -F " " '{print $2}' file | cut -d '=' -f2
Because 'fstype' argument position and file content can differ, how to do the same things and keep compatibility in shell script ?

Answer 1

Could you please try following.
awk 'match($0,/fstype=[^ ]*/){print substr($0,RSTART+7,RLENGTH-7)}' Input_file
OR more specifically to handle any string before = try following:
awk '
match($0,/fstype=[^ ]*/){
val=substr($0,RSTART,RLENGTH)
sub(/.*=/,"",val)
print val
val=""
}
' Input_file
With sed:
sed 's/.*fstype=\([^ ]*\).*/\1/' Input_file
awk code's explanation:
awk ' ##Starting awk program from here.
match($0,/fstype=[^ ]*/){ ##Using match function to match regex fstype= till first space comes in current line.
val=substr($0,RSTART,RLENGTH) ##Creating variable val which has sub-string of current line from RSTART to till RLENGTH.
sub(/.*=/,"",val) ##Substituting everything till = in value of val here.
print val ##Printing val here.
val="" ##Nullifying val here.
}
' Input_file ##mentioning Input_file name here.

Answer 2

Any time you have tag=value pairs in your data I find it best to start by creating an array (f[] below) that maps those tags (names) to their values:
$ awk -v tag='fstype' -F'[ =]' '{for (i=2;i<NF;i+=2) f[$i]=$(i+1); print f[tag]}' file
sd
$ awk -v tag='console' -F'[ =]' '{for (i=2;i<NF;i+=2) f[$i]=$(i+1); print f[tag]}' file
ttymxc1,115200
With the above approach you can do whatever you like with the data just by referencing it by it's name as the index in the array, e.g.:
$ awk -F'[ =]' '{
for (i=2;i<NF;i+=2) f[$i]=$(i+1)
if ( (f["show"] == "true") && (f["timeout"] < 20) ) {
print f["console"], f["fstype"]
}
}' file
ttymxc1,115200 sd
If your data has more than 1 row and there can be different fields on each row (doesn't appear to be true for your data) then add delete f as the first line of the script.

Answer 3

If the key and value can be matched by the regex fstype=[^ ]*, grep and -o option which extracts matched pattern can be used.
$ grep -o 'fstype=[^ ]*' file
fstype=sd
In addition, regex \K can be used with -P option (please make sure this option is only valid in GNU grep).
Patterns that are to the left of \K are not shown with -o.
Therefore, below expression can extract the value only.
$ grep -oP 'fstype=\K[^ ]*' file
sd