gsub not works while or lookahead and normal pattern

[fish2bird]

Describe the bug

I want output capture pattern if matched else empty
example input

not a cd cmd
cd /ok

I want extract /ok which follows cd , and replace invalid lines to empty, expected

""
"/ok"

my try is jq -nR 'inputs|gsub("^(?!cd ).*$|^cd "; "")'
^(?!cd ).*$ works, ^cd also works, but failed while out them together.

To Reproduce

[root build]#(echo "not a cd cmd"; echo "cd /ok") | ./jq -nR 'inputs|gsub("^cd "; "")'
"not a cd cmd"
"/ok"
[root build]#(echo "not a cd cmd"; echo "cd /ok") | ./jq -nR 'inputs|gsub("^(?!cd ).*$"; "")'
""
"cd /ok"
[root build]#(echo "not a cd cmd"; echo "cd /ok") | ./jq -nR 'inputs|gsub("^(?!cd ).*$|^cd "; "")'
""
""

Expected behavior

jq works likes perl

[root build]#(echo "not a cd cmd"; echo "cd /ok")
not a cd cmd
cd /ok
[root build]#(echo "not a cd cmd"; echo "cd /ok") | perl -pe 's/^(?!cd ).*$|^cd //g'

/ok
[root build]#

Environment (please complete the following information):

• OS: CentOS 7
• jq version: jq-1.6

Additional context

[pkoppstein]

Use sub, not gsub. gsub interprets ^ naively.

[fish2bird]

Use sub, not gsub. gsub interprets ^ naively.

[root build]#(echo "not a cd cmd"; echo "cd /ok") | ./jq -nR 'inputs|sub("^(?!cd ).*$|^cd "; ""; "")'
""
"/ok"

But, My final aim is to replace multi occurrences in a line,
for example cd asdf; cd bbbb; cd ddd to asdf;bbbb;ddd

I also checked sub(pattern; tostring; "g"), which failed as gsub

[root build]#(echo "not a cd cmd"; echo "cd /ok") | ./jq -nR 'inputs|sub("^cd "; ""; "g")'
"not a cd cmd"
"/ok"
[root build]#(echo "not a cd cmd"; echo "cd /ok") | ./jq -nR 'inputs|sub("^(?!cd ).*$"; ""; "g")'
""
"cd /ok"
[root build]#(echo "not a cd cmd"; echo "cd /ok") | ./jq -nR 'inputs|sub("^(?!cd ).*$|^cd "; ""; "g")'
""
""

[pkoppstein]

@chencang1980 wrote:

My final aim is to replace multi occurrences in a line

So if you want to use jq, you'll either have to write your own gsub or choose a different parsing strategy. How about splitting on the ';'? Or if you want a purely-regex approach:

def sub:
  if . == null then empty
  elif length == 0 then .
  else capture("^( *cd  *)?(?<dir>[^;]*)(;(?<etc>.*))?")
  | .dir, (.etc|sub)
  end;

[fish2bird]

you'll either have to write your own gsub or choose a different parsing strategy

Thank you, My final workaround is capture + sed:

make_to_compile_commands_json ()
{
    make --always-make --dry-run \
        | grep -wE '^(cd .* && )?/?(\w+/)*(gcc|g\+\+|cc|c\+\+) .*-c ' \
        | ${JQ_PATH:-jq} -nR '[inputs|capture("^(cd (?<directory>.*) && )?(?<command>.* (?<file>[^ \\t]+))$")]' \
        | sed -e 's/: null,$/: ".",/g' \
        > compile_commands.json
}

There may be many traps in sub/gsub, whose document just say as PCRE......
Will document change or code change?

[itchyny]

Inaccurate documentation about PCRE was raised by #2439 before. No PR fixing this was created though.

[pkoppstein]

@itchyny - This issue (specifically jq -nR 'inputs|gsub("^(?!cd ).*$|^cd "; "")') is resolved by PR #2624