How can i read the contents of multiple files?

Question

I need to read the contents of multiple files, for now I can read the contents of just one file using the code below , this code further reads the contents present in "rules1.txt" using "strings" . I just need the same functionality but with multiple files to read in "apps.txt" .

for i in $(cat apps.txt);
do    
cd /local/apps/oracle/Middleware/user_projects/epmsystem1/EssbaseServer/essbaseserver1/app/$i
echo $i >> /data/shellscripts/essbase/Operate/Overlays/rules1.txt     done
for i in $(ls *.rul);do
echo $i  >> /data/shellscripts/essbase/Operate/Overlays/rules1.txt      
strings $i  >> /data/shellscripts/essbase/Operate/Overlays/rules.txt

Solution

Don't read the whole apps.txt file into a for loop. In the general case, this could cause memory issues if the file is huge, and it would cause issues if any filename in apps.txt had spaces in them. Don't loop over the output of ls. Also, quote variable expansions and use printf for outputting variable data.

Related:

• Why *not* parse `ls`?
• Why is printf better than echo?
• Why does my shell script choke on whitespace or other special characters?
• Security implications of forgetting to quote a variable in bash/POSIX shells

Suggestion:

#!/bin/sh

appdir='/local/apps/oracle/Middleware/user_projects/epmsystem1/EssbaseServer/essbaseserver1/app'
outdir='/data/shellscripts/essbase/Operate/Overlays'

while IFS= read -r app; do
    printf '%s\n' "$app"
    for name in "$appdir/$app"/*.rul; do
        printf '%s\n' "${name##*/}"
        strings "$name"
    done
done <apps.txt >"$outdir/rules1.txt"

This would read app from the apps.txt file and would access all the *.rul files in the corresponding subdirectory under $appdir. The strings $app and ${name##*/} (the basename of the current *.rul file) would be outputted in each iteration, along with the output of strings. The output would go to the $outdir/rules1.txt file.

Also related (to my solution):

• Understanding "IFS= read -r line"

Comments

[S edwards]

for i in $(ls *.rul); you should never use ls result. use for i in *.rul this will work better and on all linux you will use your script on. unix.stackexchange.com/q/128985/53092

[user3851659]

its unable to recognize the files within apps.txt with while

[S edwards]

What you mean ? What is not working how it's not working ?