POSIX is an acronym for "Portable Operating System Interface", a family of standards specified by the IEEE for maintaining compatibility between operating systems.

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What is the safest (or most elegant or shortest) way to change to the directory from where a script is called?

I wondered what might be a safe or the Unix compatible way to change to the directory from which a script is called. These two methods even work in a directory with spaces and special characters in ...
16
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4answers
790 views

checkbashisms-compliant way to determine the current shell

In my .profile, I use the following code to ensure that Bash-related aliases and functions are only sourced if the login shell actually is Bash: # If the current (login) shell is Bash, then if [ "${...
11
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4answers
15k views

find -exec in bash script with variable expansion

I'm trying to run a command similar to the one below in a bash script. It should search through all subfolders of $sourcedir and copy all files of a certain type to the root level of $targetdir. #!/...
4
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1answer
96 views

Is the $SHELL environment variable only for interactive shells?

I see two possible uses for the SHELL environment variable: It can be used to specify the interactive shell the user wants to use, and/or it can be used by processes to execute other commands with, ...
0
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2answers
129 views

POSIX regular expression match on first occurrence of string

I have bash script I only want to support long options ("--option"). An --option can optionally have one or more arguments. All words (anything delimited by whitespace) up to but not including the ...
4
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2answers
118 views

Is a sub-shell the same thing as a child-shell

There are this two names: a subshell and a child-shell. Yes, a child process will be started by any of this: sh -c 'echo "Hello"' ( echo "hello" ) echo "$(echo "hello") echo "hello" | cat Are all ...
13
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4answers
11k views

sed on OSX insert at a certain line

So I've been using 'sed' on linux for a while, but have had a bit of difficulty trying to use it on OSX since 'POSIX sed' and 'GNU sed' have so many little differences. Currently I'm struggling with ...
0
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0answers
27 views

`getaddrinfo`: what specifies its data source in the POSIX standard?

I wanted to check getaddrinfo is expected to use Unbound when it's installed. Unless I overlooked something in this specification, it does not refer to any data sources it is required to check: ex. no ...
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1answer
123 views

Simple bash script to print prime numbers from 1 to 1000 [closed]

How can I make a POSIX script that will print all the prime numbers from 1 to 1000? Lots of thanks
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2answers
28 views

Should the operands to a utility always appear after all the options to the utility?

POSIX says utility_name[-a][-b][-c option_argument] [-d|-e][-f[option_argument]][operand...] ... The arguments following the last options and option-arguments are named "operands". ...
4
votes
3answers
155 views

Force POSIX mode

Brace Expansion, eg {a,b,c} is not defined by POSIX. I would like to run my shell in POSIX mode. With Debian this is simple enough: $ bash -c 'echo {a,b,c}' a b c $ sh -c 'echo {a,b,c}' {a,b,c} ...
3
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7answers
568 views

Check if shell variable contains an absolute path

I want to check if a shell variable contains an absolute path. I don't care if the path exists or not—if it doesn't I'm going to create it—but I do want to ensure that I'm dealing with an absolute ...
1
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0answers
27 views

Why are there no LSM hooks in the POSIX IPC APIs?

As I understand it, the Linux Security Module (LSM) framework has many hooks which are callbacks for security modules to register functions performing additional security checks before security-...
2
votes
2answers
2k views

How to install php7 modules in archlinux?

I have the following php version installed: PHP 7.0.2 (cli) (built: Jan 6 2016 11:50:59) ( NTS ) Copyright (c) 1997-2015 The PHP Group Zend Engine v3.0.0, Copyright (c) 1998-2015 Zend Technologies ...
2
votes
2answers
398 views

uname -n vs hostname

What is the difference between uname -n and hostname? Are there any real differences in what they return? Are there any differences in availability on different OSes? Is one of them included in POSIX ...
8
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2answers
76 views

What does [[.ch.]] mean in a regex?

Alternate title: What is a "collating sequence" or "collating element" in a POSIX-compliant regex? I found the exact technical definition in Section 9.3.5 of the POSIX specs, as item #4 in the list, ...
3
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2answers
48 views

Parameter expansion on multiple variables

Parameter expansion on a single variable works as expected. But how to expand parameters that comprise several variables? Example: #!/bin/sh foo=/lorem/ipsum; bar=dolor/sit tmp="$foo/$bar" printf '%...
37
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1answer
3k views

Does 'rm .*' ever delete the parent directory?

The expression .* is expanded by bash to include the current and parent directories: $ ls -la total 2600 drwxrwxrwx 2 terdon terdon 2162688 Sep 10 16:22 . drwxr-xr-x 142 terdon terdon 491520 Sep ...
2
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1answer
104 views

Why POSIX left `$(expression)` in awk unspecified?

Answering this question, I found that in: echo 1 2 | awk '{print $(expression)}' the return value of expression is unspecified. It can lead to confusion, as if expression is an uninitialized ...
3
votes
1answer
69 views

`EINTR`: is there a rationale behind it?

Small talk as background EINTR is the error which so-called interruptible system calls may return. If a signal occurs while a system call is running, that signal is not ignored and a signal handler ...
3
votes
1answer
353 views

Get output of `posix_spawn`

So I can run a process in Unix / Linux using POSIX, but is there some way I can store / redirect both the STDOUT and STDERR of the process to a file? The spawn.h header contains a deceleration of ...
8
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2answers
171 views

Variable assignments affect present running shell

While writing some code I found out that this line: $ TZ="America/Los_Angeles" date; echo "$TZ" Thu Dec 24 14:39:15 PST 2015 Correctly gives the actual time at "Los Angeles" and that the ...
4
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1answer
226 views

In POSIX sed, does the period (dot) match a newline in a multiline pattern space?

In GNU sed it works. For example, this matches two blank lines in a multiline pattern space (created with N) /^\n$/ Is this standard?
5
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1answer
182 views

Does POSIX sh allow empty compound-list in first condition and empty condition in case conditional construct?

Reading POSIX specification for case conditional construct, I see: case word in [(]pattern1) compound-list;; [[(]pattern[ | pattern] ... ) compound-list;;] ... [[(]pattern[ | pattern] ... ...
4
votes
1answer
367 views

Why GNU find -execdir command behave differently than BSD find?

On my OSX, I've installed GNU find next to default BSD find via: brew install findutils. As far as I understand, BSD find is following POSIX standards and GNU makes it optional (as per this post), ...
36
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7answers
3k views

Is test or [ or [[ more portable both between bash shells and between other shells?

I see I can do $ [ -w /home/durrantm ] && echo "writable" writable or $ test -w /home/durrantm && echo "writable" writable or $ [[ -w /home/durrantm ]] && echo "writable"...
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0answers
22 views

The SUS v4 would not be able to certify Bell Labs unix v8 because unix has changed right?

I am not an an expert, so I would appreciate it if someone would clarify to me about how UNIX v8 from Bell Labs might not be able to certify with the Single Unix Specification v4 because UNIX has ...
2
votes
2answers
49 views

alphabetical expansion order for *

When I'm using a POSIX compliant shell (es: dash, bash, zsh, ...) can I be sure that * will always expand in alphabetical order (dictated by LC_COLLATE)? example: $ echo 1 > file_a $ echo 2 > ...
2
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2answers
38 views

How can I get FreeBSD `patch` to tolerate null bytes?

The patch of the final line fails on FreeBSD 10.2, but works on GNU: #!/bin/sh echo a > f1 printf '\0' >> f1 echo c >> f1 cp f1 f2 echo d >> f2 diff -au f1 f2 > diff patch <...
1
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0answers
63 views

When using linux acl mkdir and mkdir -p do different things

I have a directory bar: # file: bar/ # owner: root # group: root user::rwx user:little-jonny:rwx group::r-x mask::rwx other::r-x default:user::rwx default:user:little-jonny:rwx default:group::r-x ...
4
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1answer
72 views

Is this tail behavior in Grouping Commands specified by POSIX?

Using tail combined with other standard tools in Grouping Commands can make some powerful constructions. For example, to get the first and last line of a file: $ seq 10 > file $ { head -n1; tail -...
2
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1answer
62 views

Why does cd-ing to // set PWD to //, but more slashes just gives /? [duplicate]

On my ubuntu box I accidentally just did cd // and noticed that my current path changed to //. ls showed the contents of my root directory. When I try cd /// (or any other number of slashes) I'm just ...
1
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1answer
68 views

Is it safe to ignore O_DIRECT?

I am going to implement a filesystem in FUSE, and later in the kernel. I am not sure what to make out of Direct IO. Different sources emphasize on different things that this flag supposedly implies. ...
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votes
1answer
55 views

What is posix, and how can I elevate my permissions using python? [closed]

I was wondering if I could elevate my permissions on a chromebook with the os posix using a python script. I was not given the administrative permissions when I was given the laptop for college.
2
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1answer
103 views

How to combine POSIX character classes of a regex?

I need to combine different character classes in a regular expresion used by sed. I need to match [:word:] and the minus symbol -. How does that look like? All my attempts failed at trying or ...
7
votes
4answers
576 views

Looking for POSIX utility to test whether filename is a symlink

I know that some shells at least support file test operators that detect when a filename names a symlink. Is there a POSIX utility1 that provides the same functionality? 1 I may not be using the ...
2
votes
2answers
54 views

What are the POSIX “mandatory utilities”?

For some reason, when it comes to POSIX, I always have a hard time finding the full scoop. For example, the POSIX docs (here and here) refer to "mandatory utilities", but I can't find any listing of ...
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2answers
112 views

Change time format in a file

I have output of a sar commands and the time is not POSIX: Linux 2.6.32-431.29.2.el6.x86_64 (test.server.com) 2015-08-01 _x86_64_ (32 CPU) 12:00:01 AM CPU %usr %nice %sys %...
10
votes
2answers
275 views

How to open grep(1p) manpage?

At the end of man grep, it says SEE ALSO\ POSIX Programmer's Manual Page grep(1p). I am not able to open the manpage grep(1p). How do I do that? Search net, Unix.SE and did trial and ...
1
vote
3answers
95 views

New signal arrives while execution is in a signal handler, how to decide which is first?

I am working on a tool handling a massive amount of signals (with different signums) with sigaction(). I need to handle the case, if a new signal is coming, while the previous was in a signal handler....
6
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2answers
286 views

Why do Linux/POSIX have lchown but no lchmod?

It seems that Linux supports changing the owner of a symbolic link (i.e. lchown) but changing the mode/permission of a symbolic link (i.e. lchmod) is not supported. As far as I can see this is in ...
3
votes
1answer
354 views

POSIX head and tail not feature equivalent

The documentation for POSIX tail's -n option says that The origin for counting shall be 1; that is, -n +1 represents the first line of the file, -n -1 the last. So tail -n 10 (used later on the ...
1
vote
1answer
53 views

How reliable/portable are Nix built-ins/commands (echo, ps, sort, uniq) from Debian to other distros

I've coded a script and am wondering about it's reliability / portability. #!/bin/bash threadsPlease() { ps -mo lwp,c -p $1 | sort -gk 2 | uniq -f 1 } THREAD_LINE=$( threadsPlease $1 | grep -v - |...
0
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1answer
148 views

Linux UART IO File

How bytes received on UART device are stored in some serial Linux devices /dev/ttyS? How to read them? What is the procedure? Should that device file be closed, when new data is arriving?
2
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0answers
385 views

What happens to a multithreaded Linux process if it gets a signal?

If a Unix (Posix) process receives a signal, a signal handler will run. What will happen to it in a multithreaded process? Which thread receives the signal? On my opinion, the signal API should be ...
1
vote
1answer
139 views

Reading input fields separated by spaces

How can I read in POSIX bash input like this: <name>,<tag1> <tag2> <tag3>… I tried while read line;do done but this wants newlines, all I have is spaces. (Is IFS solution? ...
30
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8answers
5k views

What's the difference of the Userland vs the Kernel?

I am trying to understand exactly what is userland? everyone that I ask says: "Anything that is not kernel". but it is not tangible for me. When I am reading that kernel can run that driver on the ...
5
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2answers
62 views

posix placement of stdin redirection (<in cmd vs cmd <in)

I always write stdin redirection after the command, because for me it's more natural to have first the command and then the redirections (if any): some-command < input-file > output-file For ...
4
votes
1answer
310 views

POSIX behavior of sed's ^ and $ regex anchors with multiline pattern spaces

What is the POSIX behavior of the sed ^ and $ anchors when used at the beginning and end of a regex if the pattern space contains embedded newlines, like after you use the N command? Should they ...
4
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1answer
240 views

awk/nawk alternative on SunOs and Linux

I have a script that basically checks the Java version on the box it's running on and does whatever based on the version number. My problem is that I want to use the same command on both SunOs and ...