Awk from getting started to digging in (23) awk built-in variables argc, argc -- command line parameter transfer

awk Can pass -v var=value In the form of awk The script passes variables , Except in this way , You can also directly awk Pass directly on the command line , Such as ：

$ echo a | gawk 'BEGIN{ for(i = 0 ; i < ARGC; i++) print ARGV[i]}' xx
gawk
xx

awk Two built-in variables are provided ,ARGC Indicates the number of command line parameters ,ARGV Is an array of command line parameters , Size by ARGC instructions .

Be careful , Names are case sensitive .

But , We found that , If you add a non BEGIN sentence , Then there will be mistakes ：

$ echo a | gawk  'BEGIN{ for(i = 0 ; i < ARGC; i++) print ARGV[i]} {}' xx
gawk
xx
gawk: cmd. line:1: fatal: cannot open file `xx' for reading: No such file or directory

awk It seems that the following parameters are used as the name of the file to be processed .

The real reason is awk Will be read in turn ARGV Elements of array , Treat it as the name of the file to be processed .

Fortunately, , We can modify ARGV Array to avoid this problem .

Direct reduction ARGC Value , It can lead to awk Will not read some files at the end . Besides , Increase or decrease ARGC Value , Will not affect ARGV Array , Just influence awk Number of read files .

# ARGC The value of is 3, Modified into 2, Don't read b.txt
awk 'BEGIN{ARGC=2}{print}' a.txt b.txt