File Checking (The GNU Awk User’s Guide)
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10.3.3 Checking for Readable Data files
Normally, if you give awk
a data file that isn’t readable, it stops with a fatal error. There are times when you might want to just ignore such files and keep going.72 You can do this by prepending the following program to your awk
program:
# readable.awk --- library file to skip over unreadable files BEGIN { for (i = 1; i < ARGC; i++) { if (ARGV[i] ~ /^[a-zA-Z_][a-zA-Z0-9_]*=.*/ \ || ARGV[i] == "-" || ARGV[i] == "/dev/stdin") continue # assignment or standard input else if ((getline junk < ARGV[i]) < 0) # unreadable delete ARGV[i] else close(ARGV[i]) } }
This works, because the getline
won’t be fatal. Removing the element from ARGV
with delete
skips the file (because it’s no longer in the list). See also Using ARGC and ARGV.
Because awk
variable names only allow the English letters, the regular expression check purposely does not use character classes such as ‘[:alpha:]
’ and ‘[:alnum:]
’ (see section Using Bracket Expressions).
Footnotes
(72)
The BEGINFILE
special pattern (see section The BEGINFILE and ENDFILE Special Patterns) provides an alternative mechanism for dealing with files that can’t be opened. However, the code here provides a portable solution.