当awk中的模式规则不正确时执行的命令，怎么了？

Question

A strange awk phenomenon again.. (this happens all the time :) )
I have a file aaa below.

[first]
aaa
bbb
[second]
ccc
ddd
eee
[third]
fff
ggg
hhh
iii

I'm trying to print the line numbers of each section which starts with a header embraced in bracket. So I wrote a simple awk script CntSecLines.awk below(it's being debugged, so with some prints).

 /\[/{print "header found : "; print $keep " : " cnt; keep=$1; cnt=0}
!/\[/{print "header not found"; cnt = cnt+1; print "keep = " $keep;}

Below is the exection result for aaa.

ckim@stph45:~/test] awk -f CntSecLines.awk aaa
header found : 
[first] : 
header not found
keep = aaa
header not found
keep = bbb
header found : 
[second] : 2
header not found
keep = ccc
header not found
keep = ddd
header not found
keep = eee
header found : 
[third] : 3
header not found
keep = fff
header not found
keep = ggg
header not found
keep = hhh
header not found
keep = iii

I intended it to be updated only when there is the section header. But why is the variable 'keep' updated every line? when I print the variable $keep, we can see it's being updated every non-section-header line.

Answer 1

It's awk , not bash . In awk you don't use $ to get variable value (well, with exceptions, like for positional arguments $1 , $2 ...).

awk '
   /\[/{print "header found : "; print keep " : " cnt; keep=$1; cnt=0}
   !/\[/{print "header not found"; cnt = cnt+1; print "keep = " keep;}
' <<EOF
[first]
aaa
bbb
[second]
ccc
ddd
eee
[third]
fff
ggg
hhh
iii
EOF

will output:

header found : 
 : 
header not found
keep = [first]
header not found
keep = [first]
header found : 
[first] : 2
header not found
keep = [second]
header not found
keep = [second]
header not found
keep = [second]
header found : 
[second] : 3
header not found
keep = [third]
header not found
keep = [third]
header not found
keep = [third]
header not found
keep = [third]

Tested on repl .

I believe awk interprets $keep as, like, $ with a string [blabla] , like $"[blabla]" , then "[blabla]" is converted from a string to a number, which results in 0 , so $keep is interpreted as $0 , which prints the whole line.

Answer 2

I interpreted your requirement as "count the lines in each bracket-delimited section."

$ awk '/^\[.*\]$/ {c=0; print; next} {print ++c, $0}' file
[first]
1 aaa
2 bbb
[second]
1 ccc
2 ddd
3 eee
[third]
1 fff
2 ggg
3 hhh
4 iii

• /^\\[.*\\]$/ - If the record begins with a literal [ and ends with a literal ]

• {c=0; print; next} {c=0; print; next} - Set/reset count, print record, skip remaining rules

• {print ++c, $0} For records not matching the first rule, print a pre-incremented count, the Output Field Separator , and the record $0 .