text processing - Extract certain part of filename in Bash -

i have many files in folder:

yyyymmdd_hhmmss.mp4 yyyymmdd_hhmmss_suffix1.mp4 yyyymmdd_hhmmss_suffix1_suffix2.mp4 

the following filename formats possible (rarely):

yyyymmdd_hhmmss_$$$.mp4 yyyymmdd_hhmmss_$$$_suffix1.mp4 yyyymmdd_hhmmss_$$$_suffix1_suffix2.mp4 yyyymmdd_hhmmss_$$.mp4 yyyymmdd_hhmmss_$$_suffix1.mp4 yyyymmdd_hhmmss_$$_suffix1_suffix2.mp4 yyyymmdd_hhmmss_$.mp4 yyyymmdd_hhmmss_$_suffix1.mp4 yyyymmdd_hhmmss_$_suffix1_suffix2.mp4 

where $ number 0-9

i trying catch "yyyymmdd_hhmmss" , use argument. when 1 suffix presented:

for file in "$@";    file_nosuffix="${file%*_suffix1.mp4}.mp4"   echo "$file , $file_nosuffix" done 

but lost when sorts of filename formats mentioned above presented. ideally stick current pattern:

for file in "$@";     #catch "yyyymmdd_hhmmss"    #do on files yyyymmdd_hhmmss.mp4    #do else on files yyyymmdd_hhmmss_suffix1.mp4    #etc. done 

is possible?

bash has built-in regex support, if want confirm format:

regex='^[[:digit:]]{8}_[[:digit:]]{6}' # posix ere; can't use pcre extensions here  file;   if [[ $file =~ $regex ]];     echo "${bash_rematch[0]} substring $file" >&2   else     echo "$file match required format" >&2   fi done 

one can trivially take prefix;

for file;   prefix=${file:0:15}   echo "prefix $file $prefix" done 

...or, delete last 2 underscores , after them:

prefix=${file%_*_*} 

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see:

• bashfaq #100 ("how can string manipulations in bash?")
• parameter expansion