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| -rw-r--r-- | gemfeed/2021-11-29-bash-golf-part-1.html | 29 | ||||
| -rw-r--r-- | gemfeed/atom.xml | 31 | ||||
| -rw-r--r-- | gemfeed/index.html | 2 |
3 files changed, 58 insertions, 4 deletions
diff --git a/gemfeed/2021-11-29-bash-golf-part-1.html b/gemfeed/2021-11-29-bash-golf-part-1.html index 415654d0..075b5de8 100644 --- a/gemfeed/2021-11-29-bash-golf-part-1.html +++ b/gemfeed/2021-11-29-bash-golf-part-1.html @@ -19,7 +19,7 @@ jgs^^^^^^^`^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Art by Joan Stark </pre> -<p class="quote"><i>Published by Paul Buetow 2021-11-29</i></p> +<p class="quote"><i>Published by Paul Buetow 2021-11-29, last updated 2022-01-05</i></p> <p>This is the first blog post about my Bash Golf series. This series is about random Bash tips, tricks and weirdnesses I came across. It's a collection of smaller articles I wrote in an older (in German language) blog, which I translated and refreshed with some new content.</p> <a class="textlink" href="./2021-11-29-bash-golf-part-1.html">Bash Golf Part 1 (you are reding this atm.)</a><br /> <a class="textlink" href="./2022-01-01-bash-golf-part-2.html">Bash Golf Part 2</a><br /> @@ -142,6 +142,33 @@ foo bar baz > ^C </pre> <p>In case you know more (subtle) differences, please write me an E-Mail and let me know.</p> +<p class="quote"><i>Update: A reader sent me an E-Mail and pointed me to the Bash manual page, which explains the difference between () and {} (I should have checked that by myself):</i></p> +<pre> +(list) list is executed in a subshell environment (see COMMAND EXECUTION ENVIRONMENT + below). Variable assignments and builtin commands that affect the shell's + environment do not remain in effect after the command completes. The return + status is the exit status of list. + +{ list; } + list is simply executed in the current shell environment. list must be ter‐ + minated with a newline or semicolon. This is known as a group command. The + return status is the exit status of list. Note that unlike the metacharac‐ + ters ( and ), { and } are reserved words and must occur where a reserved word + is permitted to be recognized. Since they do not cause a word break, they + must be separated from list by whitespace or another shell metacharacter. +</pre> +<p>So I was right that () is executed in a subprocess. But why does $$ not show a different PID? Also here (as pointed out by the reader) is the answer in the manual page:</p> +<pre> +$ Expands to the process ID of the shell. In a () subshell, it expands to the + process ID of the current shell, not the subshell. +</pre> +<p>If we want print the subprocess PID, we can use the BASHPID variable:</p> +<pre> +❯ echo $BASHPID; { echo $BASHPID; }; ( echo $BASHPID; ) +1028465 +1028465 +1028739 +</pre> <h2>Expansions</h2> <p>Let's start with simple examples:</p> <pre> diff --git a/gemfeed/atom.xml b/gemfeed/atom.xml index c26684af..73fd6b3f 100644 --- a/gemfeed/atom.xml +++ b/gemfeed/atom.xml @@ -1,6 +1,6 @@ <?xml version="1.0" encoding="utf-8"?> <feed xmlns="http://www.w3.org/2005/Atom"> - <updated>2022-01-03T10:59:45+00:00</updated> + <updated>2022-01-05T21:44:28+00:00</updated> <title>snonux.de feed</title> <subtitle>Having fun with computers!</subtitle> <link href="https://snonux.de/gemfeed/atom.xml" rel="self" /> @@ -521,7 +521,7 @@ PAUL:X:1000:1000:PAUL BUETOW:/HOME/PAUL:/BIN/BASH jgs^^^^^^^`^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Art by Joan Stark </pre> -<p class="quote"><i>Published by Paul Buetow 2021-11-29</i></p> +<p class="quote"><i>Published by Paul Buetow 2021-11-29, last updated 2022-01-05</i></p> <p>This is the first blog post about my Bash Golf series. This series is about random Bash tips, tricks and weirdnesses I came across. It's a collection of smaller articles I wrote in an older (in German language) blog, which I translated and refreshed with some new content.</p> <a class="textlink" href="https://snonux.de/gemfeed/2021-11-29-bash-golf-part-1.html">Bash Golf Part 1 (you are reding this atm.)</a><br /> <a class="textlink" href="https://snonux.de/gemfeed/2022-01-01-bash-golf-part-2.html">Bash Golf Part 2</a><br /> @@ -644,6 +644,33 @@ foo bar baz > ^C </pre> <p>In case you know more (subtle) differences, please write me an E-Mail and let me know.</p> +<p class="quote"><i>Update: A reader sent me an E-Mail and pointed me to the Bash manual page, which explains the difference between () and {} (I should have checked that by myself):</i></p> +<pre> +(list) list is executed in a subshell environment (see COMMAND EXECUTION ENVIRONMENT + below). Variable assignments and builtin commands that affect the shell's + environment do not remain in effect after the command completes. The return + status is the exit status of list. + +{ list; } + list is simply executed in the current shell environment. list must be ter‐ + minated with a newline or semicolon. This is known as a group command. The + return status is the exit status of list. Note that unlike the metacharac‐ + ters ( and ), { and } are reserved words and must occur where a reserved word + is permitted to be recognized. Since they do not cause a word break, they + must be separated from list by whitespace or another shell metacharacter. +</pre> +<p>So I was right that () is executed in a subprocess. But why does $$ not show a different PID? Also here (as pointed out by the reader) is the answer in the manual page:</p> +<pre> +$ Expands to the process ID of the shell. In a () subshell, it expands to the + process ID of the current shell, not the subshell. +</pre> +<p>If we want print the subprocess PID, we can use the BASHPID variable:</p> +<pre> +❯ echo $BASHPID; { echo $BASHPID; }; ( echo $BASHPID; ) +1028465 +1028465 +1028739 +</pre> <h2>Expansions</h2> <p>Let's start with simple examples:</p> <pre> diff --git a/gemfeed/index.html b/gemfeed/index.html index c64fa0f2..188798c8 100644 --- a/gemfeed/index.html +++ b/gemfeed/index.html @@ -11,7 +11,7 @@ <h2>Having fun with computers!</h2> <a class="textlink" href="./2022-01-01-bash-golf-part-2.html">2022-01-01 (1077 words) - Bash Golf Part 2</a><br /> <a class="textlink" href="./2021-12-26-how-to-stay-sane-as-a-devops-person.html">2021-12-26 (2101 words) - How to stay sane as a DevOps person </a><br /> -<a class="textlink" href="./2021-11-29-bash-golf-part-1.html">2021-11-29 (1199 words) - Bash Golf Part 1</a><br /> +<a class="textlink" href="./2021-11-29-bash-golf-part-1.html">2021-11-29 (1281 words) - Bash Golf Part 1</a><br /> <a class="textlink" href="./2021-10-22-defensive-devops.html">2021-10-22 (2276 words) - Defensive DevOps</a><br /> <a class="textlink" href="./2021-09-12-keep-it-simple-and-stupid.html">2021-09-12 (1365 words) - Keep it simple and stupid</a><br /> <a class="textlink" href="./2021-08-01-on-being-pedantic-about-open-source.html">2021-08-01 (2919 words) - On being Pedantic about Open-Source</a><br /> |