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dtb 2021-08-18 22:53:23 -04:00
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homepage/knowledge/true.html
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@ -15,7 +15,7 @@
<SCRIPT SRC="/js/sheets.js" TYPE="application/javascript"></SCRIPT> <SCRIPT SRC="/js/sheets.js" TYPE="application/javascript"></SCRIPT>
<SCRIPT TYPE="application/javascript">window.onload = window.initializesheets;</SCRIPT> <SCRIPT TYPE="application/javascript">window.onload = window.initializesheets;</SCRIPT>
<H1>POSIX true(1)</H1> <H1>POSIX true(1)</H1>
<H3>updated 2021-08-06</H3> <H3>updated 2021-08-18</H3>
<HR ALIGN="left" SIZE="1" WIDTH="25%" /> <HR ALIGN="left" SIZE="1" WIDTH="25%" />
<P> <P>
<CODE>true(1)</CODE> is a tool that <I>only</I> quits silently with an exit status of 0. <CODE>true(1)</CODE> is a tool that <I>only</I> quits silently with an exit status of 0.
@ -32,8 +32,8 @@ int main(void) { return 0; }
</CODE></PRE> </CODE></PRE>
<P> <P>
Because executing an empty shellscript file will in most shells do nothing and return an exit status of 0, technically an empty shellscript file is a POSIX-compliant <CODE>true(1)</CODE> implementation in 0 bytes. Because executing an empty shellscript file will in most shells do nothing and return an exit status of 0, technically an empty shellscript file is a POSIX-compliant <CODE>true(1)</CODE> implementation in 0 bytes.
However (<B>TODO</B>) it's to me unknown whether this is implementation-specific or POSIX-specified. This was the <CODE>true(1)</CODE> implementation on early versions of UNIX, including Research UNIX, System V, and Sun's Solaris, according to both Rob Pike and John Chambers.
The <I>usual</I> implementation in POSIX shell is also a one-liner if you ignore the shebang: A more explicit implementation also exists in POSIX shell:
</P> </P>
<PRE><CODE CLASS="language-shell" DATA-LANG="shell"> <PRE><CODE CLASS="language-shell" DATA-LANG="shell">
#!/bin/sh #!/bin/sh
@ -60,8 +60,10 @@ Their <CODE>true.c</CODE> is 2.3 kilobytes, parses the arguments <CODE>--help</C
The GNU coreutils implementation of <CODE>true(1)</CODE> is not POSIX compliant. The GNU coreutils implementation of <CODE>true(1)</CODE> is not POSIX compliant.
</P> </P>
<H2>Cited media and further reading</H2><UL> <H2>Cited media and further reading</H2><UL>
<LI>Articles<UL> <LI>Articles and posts<UL>
<LI><A HREF="https://www.muppetlabs.com/~breadbox/software/tiny/teensy.html">Brian Raiter - A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux</A></LI> <LI><A HREF="http://trillian.mit.edu/~jc/;-)/ATT_Copyright_true.html">CHAMBERS John - The /bin/true Command and Copyright</A></LI>
<LI><A HREF="https://twitter.com/rob_pike/status/966896123548872705">PIKE Rob - "/bin/true used to be an empty file."</A></LI>
<LI><A HREF="https://www.muppetlabs.com/~breadbox/software/tiny/teensy.html">RAITER Brian - A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux</A></LI>
</UL></LI> </UL></LI>
<LI>Manual pages<UL> <LI>Manual pages<UL>
<LI><A HREF="https://www.unix.com/man-page/posix/1p/true/">true(1p)</A> (The Open Group, 2003)</LI> <LI><A HREF="https://www.unix.com/man-page/posix/1p/true/">true(1p)</A> (The Open Group, 2003)</LI>