I don’t understand what a single backtick and double quote and >> do in this script Code Answer

This example was in a Linux book:

$ cat sort-wc
#!/bin/bash
# Sort files according to their line count
for f
do
    echo `wc -l <"$f» lines in $f
done | sort -n
$ ./sort-wc /etc/passwd /ect/fstab /etc/motd

What I don’t get is why there is only a single backtick, a single double quote and what the >> does. Isn’t >> for writing to a file?

Answer

This is from page 121 of “Introduction to Linux for Users and Administrators” and that’s a typographical error in the text. The script is also avaliable in other texts from tuxcademy, with the same typographical error.

The single » character is not the same as the double >> and it serves no purpose in a shell script. My guess is that the typesetting system used for formatting the text of the book got confused by "` for some reason and formatted it as a guillemet (angle-quote), or it’s just a plain typo (the «...» quotes are used for quoting ordinary text elsewhere in the document).

The script should read

#!/bin/bash
# Sort files according to their line count
for f
do
    echo `wc -l <"$f"` lines in $f
done | sort -n

… but would be better written

#!/bin/sh
# Sort files according to their line count

for f; do
    printf '%d lines in %sn' "$(wc -l <"$f")" "$f"
done | sort -n

The backticks are an older form of $( ... ), and printf is better to use for outputting variable data. Also, variable expansions and command substitutions should be quoted, and the script uses no bash features so it could just as well be executed by /bin/sh.

Related:

• Have backticks (i.e. `cmd`) in *sh shells been deprecated?
• Why is printf better than echo?
• Security implications of forgetting to quote a variable in bash/POSIX shells
• Why does my shell script choke on whitespace or other special characters?