Bash (split) file name comparison fails - bash

Question

In my directory I have files (*fastq.gz.fasta) and directories, whose names contain the filenames (*fastq.gz.fasta-blastdb):
IVC6_Meino.clust.gz.fasta-blastdb
IVC5_Mehiv.clust.gz.fasta-blastdb
....
IVC6_Meino.clust.gz.fasta
IVC5_Mehiv.clust.gz.fasta
....
In a bash script I want to compare the filenames with the direcories using the cut option on the latter to extract only the filename part. If those two names match I want to do further stuff (for now echo match or no match respectively).
I have written the following piece of code:
#!/bin/bash
for file in *.fasta
do
for db in *-blastdb
do
echo $file, $db | cut -d '-' -f 1
if [[ $file = "$db | cut -d '-' -f 1" ]]; then
echo "match"
else
echo "no match"
fi
done
done
But it does not detect matches. The output looks like this:
...
IVC6_Meino.clust.gz.fasta, IIIA11_Meova.clust.gz.fasta
no match
IVC6_Meino.clust.gz.fasta, IVC5_Mehiv.clust.gz.fasta
no match
IVC6_Meino.clust.gz.fasta, IVC6_Meino.clust.gz.fasta
no match
The last line should read match as you can see, the strings look the same.
What am i missing?

Answer 1

You can use parameter expansion to do this more easily:
for file in *.fasta
do
for db in *-blastdb
do
echo "$file", "$db"
if [[ "${file%%.fasta}" = "${db%%.fasta-blastdb}" ]]; then
echo "match"
else
echo "no match"
fi
done
done
If you want to fix yours, the problem is the use of $db | cut -d '-' -f 1 With echo it appears that echo is printing the pipe. It isn't. cut is printing. When you do [[ $file = "$db | cut -d '-' -f 1" ]] it is equivalent to [[ $file = [return code from last pipe component] ]]
You need to use the $(..) shell construct to capture the output of the pipe and you need to echo to get the contents of $db to start the pipe. You should quote "$db" so you do not have word splitting or globbing from the contents of the variable.
Like so:
for file in *.fasta
do
for db in *-blastdb
do
ts=$(echo "$db" | cut -d '-' -f 1)
echo "$file", "$ts"
if [[ "$file" = "$ts" ]]; then
echo "match"
else
echo "no match"
fi
done
done # this works I think -- not tested...
Please be careful with your quoting with Bash and liberally use ShellCheck.
The structure you have is also not the most efficient. You will loop over the *-blastdb glob once for every file in *-blastdb. If you have a lot of files, that could get really slow.
To solve that, you could rewrite this loop with Bash arrays (best if you have Bash 4+) or use awk:
ext1=.fasta
ext2=.fasta-blastdb
awk 'FNR==NR{
s=$0
sub("\\"ext1"$","",s)
seen[s]=$0
next}
{
s=$0
sub("\\"ext2"$","",s)
if (s in seen)
print seen[s], $0
}
' ext1="$ext1" ext2="$ext2" <(for fn in *$ext1; do echo "$fn"; done) <(for fn in *$ext2; do echo "$fn"; done)
Each glob is only executing once and awk is using an array to test if the basenames are the same.
Best