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 Dec 31 '18 at 17:31
TimTim
26.3k74246455
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 Dec 31 '18 at 17:31
TimTim
26.3k74246455
5
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
Dec 31 '18 at 18:05
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 Dec 31 '18 at 17:31
TimTim
26.3k74246455
$ 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 Dec 31 '18 at 17:31
TimTim
26.3k74246455
asked Dec 31 '18 at 17:31
TimTim
26.3k74246455
edited Dec 31 '18 at 17:41
Tim
asked Dec 31 '18 at 17:31
TimTim
26.3k74246455
asked Dec 31 '18 at 17:31
TimTim
26.3k74246455
asked Dec 31 '18 at 17:31
TimTim
26.3k74246455
26.3k74246455
5
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
Dec 31 '18 at 18:05
add a comment |
5
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
Dec 31 '18 at 18:05
5
5
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
Dec 31 '18 at 18:05
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
Dec 31 '18 at 18:05
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 Dec 31 '18 at 17:41
DopeGhotiDopeGhoti
43.6k55382
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 Dec 31 '18 at 17:36
glenn jackmanglenn jackman
50.4k570107
add a comment |
Your Answer
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "106"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f491793%2fwhy-is-this-string-matching-condition-in-not-true%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
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 Dec 31 '18 at 17:41
DopeGhotiDopeGhoti
43.6k55382
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 Dec 31 '18 at 17:41
DopeGhotiDopeGhoti
43.6k55382
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 Dec 31 '18 at 17:41
DopeGhotiDopeGhoti
43.6k55382
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 Dec 31 '18 at 17:41
DopeGhotiDopeGhoti
43.6k55382
edited Dec 31 '18 at 17:47
answered Dec 31 '18 at 17:41
DopeGhotiDopeGhoti
43.6k55382
answered Dec 31 '18 at 17:41
DopeGhotiDopeGhoti
43.6k55382
answered Dec 31 '18 at 17:41
DopeGhotiDopeGhoti
43.6k55382
43.6k55382
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 Dec 31 '18 at 17:36
glenn jackmanglenn jackman
50.4k570107
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 Dec 31 '18 at 17:36
glenn jackmanglenn jackman
50.4k570107
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 Dec 31 '18 at 17:36
glenn jackmanglenn jackman
50.4k570107
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 Dec 31 '18 at 17:36
glenn jackmanglenn jackman
50.4k570107
answered Dec 31 '18 at 17:36
glenn jackmanglenn jackman
50.4k570107
answered Dec 31 '18 at 17:36
glenn jackmanglenn jackman
50.4k570107
answered Dec 31 '18 at 17:36
glenn jackmanglenn jackman
50.4k570107
50.4k570107
add a comment |
add a comment |
Thanks for contributing an answer to Unix & Linux Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f491793%2fwhy-is-this-string-matching-condition-in-not-true%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
5
always quote your variables ... then you'd see the spaces in front of the -1, as DopeGhoti pointed out
– Jeff Schaller
Dec 31 '18 at 18:05