Why is this string matching condition in [[ ]] not true?
$ tpgid=$(ps --no-headers -o tpgid -p 1)
$ echo $tpgid
-1
$ if [[ $tpgid == "-1" ]]; then
> echo "yes"
> else
> echo "no"
> fi
no
Why is the condition not true? Thanks.
$ printf "%s" "$tpgid" > /tmp/test/fff
$ hd /tmp/test/fff
00000000 20 20 20 2d 31 | -1|
00000005
bash
asked 12 hours ago
Tim
26k74246455
add a comment |
$ tpgid=$(ps --no-headers -o tpgid -p 1)
$ echo $tpgid
-1
$ if [[ $tpgid == "-1" ]]; then
> echo "yes"
> else
> echo "no"
> fi
no
Why is the condition not true? Thanks.
$ printf "%s" "$tpgid" > /tmp/test/fff
$ hd /tmp/test/fff
00000000 20 20 20 2d 31 | -1|
00000005
bash
asked 12 hours ago
Tim
26k74246455
4
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
11 hours ago
add a comment |
$ tpgid=$(ps --no-headers -o tpgid -p 1)
$ echo $tpgid
-1
$ if [[ $tpgid == "-1" ]]; then
> echo "yes"
> else
> echo "no"
> fi
no
Why is the condition not true? Thanks.
$ printf "%s" "$tpgid" > /tmp/test/fff
$ hd /tmp/test/fff
00000000 20 20 20 2d 31 | -1|
00000005
bash
asked 12 hours ago
Tim
26k74246455
$ tpgid=$(ps --no-headers -o tpgid -p 1)
$ echo $tpgid
-1
$ if [[ $tpgid == "-1" ]]; then
> echo "yes"
> else
> echo "no"
> fi
no
Why is the condition not true? Thanks.
$ printf "%s" "$tpgid" > /tmp/test/fff
$ hd /tmp/test/fff
00000000 20 20 20 2d 31 | -1|
00000005
bash
bash
asked 12 hours ago
Tim
26k74246455
asked 12 hours ago
Tim
26k74246455
edited 12 hours ago
asked 12 hours ago
Tim
26k74246455
asked 12 hours ago
Tim
26k74246455
asked 12 hours ago
Tim
26k74246455
26k74246455
4
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
11 hours ago
add a comment |
4
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
11 hours ago
4
4
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
11 hours ago
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
11 hours ago
add a comment |
2 Answers
2
active
oldest
votes
Even though [[ ... ]] is "smarter" than [ ... ] or test ..., it's still a better idea to explicitly use numerical comparison operators:
if [[ "$tpgid" -eq -1 ]]; then ...
Further, your hexdump:
$ hd /tmp/test/fff
00000000 20 20 20 2d 31 | -1|
shows that $tpgid expands to " -1", not "-1"; -eq knows how to handle this, while == is rightly doing a string comparison:
$ if [[ " -1" == -1 ]]; then echo truthy; else echo falsy; fi
falsy
$ if [[ " -1" -eq -1 ]]; then echo truthy; else echo falsy; fi
truthy
In short, the string matching condition is not returning true because the strings in fact do not match.
answered 12 hours ago
DopeGhoti
43.2k55382
add a comment |
Most likely is that $tpgid contains leading and/or trailing whitespace. Since the value is numeric, you might want to use an arithmetic expression:
if (( tpgid == -1 )); then ...
answered 12 hours ago
glenn jackman
50.3k570107
add a comment |
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2 Answers
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active
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2 Answers
2
active
oldest
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active
oldest
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active
oldest
votes
Even though [[ ... ]] is "smarter" than [ ... ] or test ..., it's still a better idea to explicitly use numerical comparison operators:
if [[ "$tpgid" -eq -1 ]]; then ...
Further, your hexdump:
$ hd /tmp/test/fff
00000000 20 20 20 2d 31 | -1|
shows that $tpgid expands to " -1", not "-1"; -eq knows how to handle this, while == is rightly doing a string comparison:
$ if [[ " -1" == -1 ]]; then echo truthy; else echo falsy; fi
falsy
$ if [[ " -1" -eq -1 ]]; then echo truthy; else echo falsy; fi
truthy
In short, the string matching condition is not returning true because the strings in fact do not match.
answered 12 hours ago
DopeGhoti
43.2k55382
add a comment |
Even though [[ ... ]] is "smarter" than [ ... ] or test ..., it's still a better idea to explicitly use numerical comparison operators:
if [[ "$tpgid" -eq -1 ]]; then ...
Further, your hexdump:
$ hd /tmp/test/fff
00000000 20 20 20 2d 31 | -1|
shows that $tpgid expands to " -1", not "-1"; -eq knows how to handle this, while == is rightly doing a string comparison:
$ if [[ " -1" == -1 ]]; then echo truthy; else echo falsy; fi
falsy
$ if [[ " -1" -eq -1 ]]; then echo truthy; else echo falsy; fi
truthy
In short, the string matching condition is not returning true because the strings in fact do not match.
answered 12 hours ago
DopeGhoti
43.2k55382
add a comment |
Even though [[ ... ]] is "smarter" than [ ... ] or test ..., it's still a better idea to explicitly use numerical comparison operators:
if [[ "$tpgid" -eq -1 ]]; then ...
Further, your hexdump:
$ hd /tmp/test/fff
00000000 20 20 20 2d 31 | -1|
shows that $tpgid expands to " -1", not "-1"; -eq knows how to handle this, while == is rightly doing a string comparison:
$ if [[ " -1" == -1 ]]; then echo truthy; else echo falsy; fi
falsy
$ if [[ " -1" -eq -1 ]]; then echo truthy; else echo falsy; fi
truthy
In short, the string matching condition is not returning true because the strings in fact do not match.
answered 12 hours ago
DopeGhoti
43.2k55382
Even though [[ ... ]] is "smarter" than [ ... ] or test ..., it's still a better idea to explicitly use numerical comparison operators:
if [[ "$tpgid" -eq -1 ]]; then ...
Further, your hexdump:
$ hd /tmp/test/fff
00000000 20 20 20 2d 31 | -1|
shows that $tpgid expands to " -1", not "-1"; -eq knows how to handle this, while == is rightly doing a string comparison:
$ if [[ " -1" == -1 ]]; then echo truthy; else echo falsy; fi
falsy
$ if [[ " -1" -eq -1 ]]; then echo truthy; else echo falsy; fi
truthy
In short, the string matching condition is not returning true because the strings in fact do not match.
answered 12 hours ago
DopeGhoti
43.2k55382
edited 11 hours ago
answered 12 hours ago
DopeGhoti
43.2k55382
answered 12 hours ago
DopeGhoti
43.2k55382
answered 12 hours ago
DopeGhoti
43.2k55382
43.2k55382
add a comment |
add a comment |
Most likely is that $tpgid contains leading and/or trailing whitespace. Since the value is numeric, you might want to use an arithmetic expression:
if (( tpgid == -1 )); then ...
answered 12 hours ago
glenn jackman
50.3k570107
add a comment |
Most likely is that $tpgid contains leading and/or trailing whitespace. Since the value is numeric, you might want to use an arithmetic expression:
if (( tpgid == -1 )); then ...
answered 12 hours ago
glenn jackman
50.3k570107
add a comment |
Most likely is that $tpgid contains leading and/or trailing whitespace. Since the value is numeric, you might want to use an arithmetic expression:
if (( tpgid == -1 )); then ...
answered 12 hours ago
glenn jackman
50.3k570107
Most likely is that $tpgid contains leading and/or trailing whitespace. Since the value is numeric, you might want to use an arithmetic expression:
if (( tpgid == -1 )); then ...
answered 12 hours ago
glenn jackman
50.3k570107
answered 12 hours ago
glenn jackman
50.3k570107
answered 12 hours ago
glenn jackman
50.3k570107
answered 12 hours ago
glenn jackman
50.3k570107
50.3k570107
add a comment |
add a comment |
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4
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
11 hours ago