Passing options like -l or --word to commands, or parsing them in scripts

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3
votes
2answers
61 views

How does the -d option to bash read work?

I have a bash script where I'm trying to assign a heredoc string to a variable using read, and it only works if I use read with the -d '' option, i.e. read -d '' <variable> script block ...
3
votes
2answers
99 views

The discrimination between short and long option is only `-`?

On Unix system, options begin with - is short option, while options begin with -- is long option. Is my understanding right?
-2
votes
1answer
33 views

What does the -p option do exactly with the cp command?

So I am trying to understand what is the significance of the -p option for the cp command. I opened the manual of the cp command and it says -p same as --preserve=mode,ownership,time stamps. But ...
2
votes
2answers
55 views

Set awk array on command line?

I know the -v switch can be used to awk on the command line to set the value for a variable. Is there any way to set values for awk associative array elements on the command line? Something like: ...
1
vote
3answers
36 views

What does the option -9 mean for killall?

I saw the command killall -9 but there is not such a option in the man page. So now I'm a bit confused: what does -9 option mean?
1
vote
1answer
50 views

Can a bash array be used in place of eval set — “$params”?

I'm taking a look at the optparse library for bash option parsing, specifically this bit in the generated code: params="" while [ $# -ne 0 ]; do param="$1" shift case "$param" in ...
1
vote
2answers
25 views

Listing negative numbers in zenity --list

$ zenity --list --column 'Numbers' '-3' This option is not available. Please see --help for all possible usages. $ zenity --list --column 'Numbers' -- '-3' So obviously zenity is interpreting the ...
0
votes
3answers
55 views

Understanding options to sort

part 1 ps -e | sort -k 1 -nr What is the interpretation of the above command? I want to understand the role of -nr. It is not clearly given the man pages of sort. part 2 When you open the man ...
3
votes
1answer
54 views

Is there a way for “less” to truncate lines and still exit after < 1 screen?

Like many (most), I use git, which by default sends its output (for diffs, logs, etc.) to less, with the options -FRSX. The options are overrideable in .gitconfig by setting the pager to be called ...
0
votes
1answer
32 views

Is a “--silent” flag supposed to suppress warnings and errors, or just warnings?

I'm designing a terminal-based application, and I want to implement a --silent flag to suppress noise if they don't want it. In this application, errors are most commonly logged when the application ...
0
votes
2answers
158 views

Linux command to display the contents of a given file byte by byte with the character and its numerical representation displayed for each byte [closed]

I am looking for the Linux command and option combination to display the contents of a given file byte by byte with the character and its numerical representation. I was under the impression that in ...
3
votes
2answers
40 views

Function with many arguments but only one switch

I am effectively making a recycling bin via some scripts I made. The first script is pretty much an alternative to the rm command (instead of actually deleting a file, it moves it to a deleted ...
6
votes
1answer
144 views

How can I delete a file named “--append”? [duplicate]

By mistake I have created a file named : --append. How do I delete it? Simply entering the usual command, rm -f --append, doesn't work.
20
votes
3answers
581 views

The precedence of command options?

I know that rm -f file1 will forcefully remove file1 without prompting me. I also know that rm -i file1 will first prompt me before removing file1 Now if you execute rm -if file1, this will also ...
1
vote
0answers
31 views

Using rsync with the verbose option and filtering the information displayed

I am using rsync with the -a -r and -v options to copy files and directories from one server to another. This all works fine. But when I make a change, for example, to a single file on the source ...
2
votes
3answers
100 views

How to read this tcpdump man page?

I am trying to use the tcpdump command in a project and I have some difficulties understanding the help page. SYNOPSIS tcpdump [ -AbdDefhgHIJKlLnNoOpPqRStuUvxX ] [ -B buffer_size ] [ -c count ] ...
1
vote
1answer
83 views

Using apropos command with -a to search multiple keywords on CentOS 7

I'm running CentOS 7.0 build 1503. I'm trying to search for commands I don't know the name of by searching the man descriptions for multiple keywords using AND (e.g. search for a command containing ...
0
votes
1answer
83 views

What's the -alhF flag in ls?

What is the -alhF flag in ls? I can't find it in the man page.
1
vote
2answers
380 views

How to extract unknown arguments within a shell script?

I have a shell script that accepts a variety of options, some with arguments, some without, some short, some long. It should handle some of these options itself and pass on the rest it does not know ...
6
votes
1answer
552 views

Why does `du -sh *` complain about invalid options?

I've searched my best through Google, but for the life of me I can't figure out what to use instead of * (asterisk) after a recent update (even Wikipedia seems to think du -sh * and du -sh * should ...
2
votes
1answer
120 views

Order between options and operands?

When using a utility program, we may specify options (and their option arguments) and/or operands. In most cases (in the sense of conforming to some standard (POSIX?)) does the order between ...
1
vote
0answers
71 views

Why is rm -r the same as rm -R?

If you look in the rm man page you see that rm -r, rm -R, and rm --recursive are all the same. -r, -R, --recursive remove directories and their contents recursively When using options, I'm ...
1
vote
2answers
106 views

how to delete file that start with “-” [duplicate]

I try to delete this file on my solaris machine rm "-Insi" rm: illegal option -- I rm: illegal option -- n rm: illegal option -- s I also try this rm "\-Insi" -Insi: No such file or directory ...
4
votes
1answer
1k views

Do you need to specify the “defaults” option in fstab?

The Arch Wiki on fstab specifies the options of / to be defaults,noatime, but on my installation the default fstab is created with the options of rw,relatime. The Arch Wiki covers the atime issues. ...
3
votes
1answer
30 views

Why did “argument can be squisehd against option” prevail over “argument is always separate”?

Inspired by the recent question Why does the specific sequence of options matter for tar command?, in which the asker learned why tar -cfv test.tar *.jpg doesn't work, I'd like to ask a followup: ...
4
votes
3answers
664 views

Why does the specific sequence of options matter for tar command?

I was trying out tar command to make archive with .tar extension. please have a look at the following series of commands I tried: $ ls abc.jpg hello.jpg xjf.jpg $ tar -cfv test.tar *.jpg tar: ...
0
votes
1answer
378 views

What does the option -C achieve in ls output?

In the man pages it says: -C list entries by columns However, I really cannot notice any difference between the output of ls or ls -C, could someone explain this to me?
5
votes
1answer
79 views

Why do some utilities parse operands before options?

According to several sources, the UNIX utility guidelines specify that operands should always be processed after options: utility_name[OPTIONS][operands...] Some older UNIX utilities are known to ...
20
votes
6answers
888 views

Is there way to see `man` document only for specified option of a command

If I want to know the meaning of wget -b, I see the manual by man wget, then search the -b option. -b --background Go to background immediately after startup. If no output file is ...
4
votes
1answer
450 views

Mapping metadata with avconv does not work

The way I understand man avconv (version 9.16-6:9.16-0ubuntu0.14.04.1), the following command should convert input.ogg to output.mp3 and carry over metadata: avconv -i input.ogg -map_metadata 0 ...
1
vote
1answer
29 views

How do I specify command invocation for a mandatory short or long option?

I'm writing a specification for a tool that needs a -f / --foo option with a mandatory argument BAR, so for example these are valid calls: tool -f BAR tool --foo BAR How do I specify this syntax in ...
17
votes
2answers
746 views

Security implications of running perl -ne '…' *

Apparently, running: perl -n -e 'some perl code' * Or find . ... -exec perl -n -e '...' {} + (same with -p instead of -n) Or perl -e 'some code using <>' * often found in one-liners ...
5
votes
2answers
4k views

Negative arguments to head / tail

Variants of this question have certainly been asked several times in different places, but I am trying to remove the last M lines from a file without luck. The second most voted answer in this ...
0
votes
2answers
26 views

why some programs needs -h and other no

I know that is not a exciting question, but yet I don't understand why some programs needs program -h and other program --help sometimes is very boring recognize it
2
votes
2answers
44 views

Is there a `--paranoid` type flag for common, potentially irreversible commands?

I'm not aware of any standard flag that is implemented. There are some git commands that let you specify a -n parameter that will show you what the command is going to do, but doesn't actually do it. ...
2
votes
1answer
137 views

Strange leading whitespace in OPTARG when using getopts

I spent quite a while researching the problem I encountered but none of the getopts tutorial say anything about the leading whitespace in OPTARG when using getopts. In bash(on Ubuntu and OSX), ...
5
votes
1answer
4k views

Provide two arguments to one option using getopts

In below code when I give option r then getopts requires one arguments: while getopts ":hr::l:" opt; do case $opt in r ) echo "Run Numbers - argument = $OPTARG " ;; l ) echo ...
2
votes
2answers
1k views

Optional arguments after or before the mandatory arguments?

I'm creating a shell script and I need it to take two mandatory arguments and one optional. How do I check that? In most scripts I've seen, the optional arguments are passed before the mandatory ones, ...
0
votes
1answer
45 views

Options to a command specified in a file

How can I have some of the options to a unix command come from a file? That is the file does not contain all the options -- other options are specified elsewhere. For example I have the ...
2
votes
1answer
167 views

FAT Mountoption allow_utime explained

I trying to figure out what the following Mountoption for (v)FAT exactly does (in Linux): allow_utime=### -- This option controls the permission check of mtime/atime. 20 - If ...
3
votes
4answers
572 views

Test if command accepts a specific option

What is the preferred way to test if a command takes an option? What are the caveats? As a motivating example, at login my shell aliases grep to add several --exclude-dir options but this option is ...
1
vote
1answer
414 views

How to know DHCP options value on debian/ubuntu and other linux

How to know all DHCP options and values (on the client side, Linux Ubuntu / Debian / ArchLinux ) provided by the server. I need to pass non-standard option to the client by the DHCP option code ...
1
vote
1answer
304 views

in which units does tar --checkpoint measure?

GNU tar offers the option --checkpoint where a message should be printed each checkpointreached. Question:: In what does --checkpoint measure? My best guess is Bytes. I wasn't able to find a hint ...
2
votes
1answer
57 views

Understanding passwd --keep-tokens

On GNU/Linux, I do have trouble understanding the meaning of the --keep-tokens option for passwd. As it doesn't seem to be much used as I am not able to find any examples and only online copies of man ...
16
votes
4answers
743 views

Why does ls accept duplicate switches?

I'm curious - is there a difference between ls -l and ls -lllllllllllllllllllllllllllll? The output appears to be the same and I'm confused on why ls allows duplicate switches. Is this a standard ...
5
votes
2answers
379 views

How do you get fgrep to find the literal “--help”?

fgrep --help | fgrep "--help" returns just the whole fgrep --help, how do I return just the lines that have the literal "--help" in them? The quotes don't do anything, nor does \-\-help.
2
votes
1answer
56 views

What is a command that will only show me the command syntax and options?

Is there a command which will just list all the options for a given command on one or two lines and not as long and words as man or info ?
3
votes
3answers
306 views

Interactive command usage reference: do you generally have that on Unix?

The question of why some commands rely on manpages whereas others rely on something like the --help flag for providing command usage reference is not new. There is usually a difference in scope ...
8
votes
1answer
2k views

How to append multiple lines to a file with bash, with “--” in front of string

Question very similar to How to append multiple lines to a file with bash but I want to start the file with --, and also append to the file, if possible. printf ...
41
votes
7answers
3k views

Is `-` used only with cd?

cd - can switch between current dir and previous dir. It seems that I have seen - used as arguments to other commands before, though I don't remember if - means the same as with cd. I found that - ...