Questions tagged [syntax]
The syntax tag has no usage guidance.
128
questions
0
votes
0answers
75 views
How does bash work? [closed]
I've done some research on how the bash shell works, and below is what I understand. Please report missing or incorrect information.
Input Stage
Shell read input.(terminal, file or argument to the ...
0
votes
0answers
45 views
What happens when we use ampersand `&` at the end of the pipeline?
Normally, when we use a pipe, the operations on the left and right of the pipe are run in separate subprocesses. The outputs of the first command are transmitted as input to the second command. In ...
1
vote
1answer
472 views
bash can't find closing bracket?
I am writing a bash script to makup the MariaDB instance on a Synology box. When I run it, it works, but I get an error:
admin@synology:/volume1/@appstore/MariaDB10/usr/local/bip$ ./mysql_backup
./...
0
votes
1answer
17 views
NVRAM Variable syntax
I'm trying to edit the client_customlist variable in my router with Merlin firmware, and am a bit confused with the syntax; when I export it and then look at it, most of them end with 3 >, like ...
2
votes
2answers
279 views
Difference between GNU find -not and GNU find -prune -o -print
This answer on opening all files in vim except [condition]:
https://unix.stackexchange.com/a/149356/98426
gives an answer similar to this:
find . \( -name '.?*' -prune \) -o -type f -print
(I adapted ...
0
votes
0answers
41 views
Conky script not running after being converted
I am attempting to convert an older conky widget to the new syntax of 1.10+, but I can't for the life of me figure out why it won't run. I've ran through everything to make sure it was converted ...
0
votes
4answers
76 views
Awk if condition error [closed]
I have written an awk command which filters based on a condition
awk '{if(( (substr($0,9,3) == "TGO") && ((substr($0,1,4) == "9123" || (substr($0,1,4) == "9704"))...
0
votes
1answer
24 views
quasi nested conditions in bash is failing, because of elif syntax error
I have code that performs some conditionals in bash:
firstchar=$(head -c 1 /tmp/project.json)
if [ $? -eq 0 ] then;
echo "Hooray! nothing found"
elif [ $? -eq 1 ]; then ...
4
votes
3answers
138 views
Compare two files on specific columns only line by line
What is the syntax inside for loop if i in [2,4,7] in awk. Also any idea how to achieve to do in below code. Thanks
Input :
$ cat f1
col1,col2,col3,col4,col5,col6,col7
col11,col12,col13,col14,col15,...
-1
votes
1answer
77 views
How to fix the error near unexpected token `else'
I am getting a syntax error at line 17 : unexpected token `else'
declare -i A
echo "enter any numeric value"
read value
if [$value > 0];
if [[ "$value" =~ ^[0-9]+$ ]]; ...
1
vote
4answers
105 views
What's the difference between if ! [[ foo ]] and if [[ ! foo ]] in Bash?
I understand that ! is used to negate an if condition in Bash, but I've just seen code which takes the format:
if ! [[ CONDITION ]]; then
SOMETHING
fi
Is there a difference between this format ...
2
votes
1answer
41 views
How do you interpret this complicated man page syntax?
I am reading this on a man page:
[-n number-to-stat[:max-size[:min-size][:num-directories[:chunk-size]]]]
I interpret this as -n is optional but how do I specify the num-directories?
Preferably I ...
-2
votes
1answer
35 views
Unifiyng lines with awk
I have the file/text bellow:
apple 1
apple 2
apple 3
banana 22
banana 5
string 1
How can I run a command to return the following result?
apple numbers:1,2,3
banana numbers:22,5
string numbers:1
-1
votes
1answer
39 views
Python Error | Basic
i tried to run this code:
cd
sudo apt-get -y install firefox
cd
wget https://github.com/mozilla/geckodriver/releases/download/v0.26.0/geckodriver-v0.26.0-linux64.tar.gz
tar xzf geckodriver-v0.25.0-...
-1
votes
1answer
36 views
How to pass brackets to some program's arguments?
I am trying to execute the command like this
python train.py --conv-layers [(512, 10, 5), (512, 8, 4)]
but bash swears
-bash: syntax error near unexpected token `('
I need train.py receive exactly ...
4
votes
3answers
456 views
Is it possible to have conditionals in /etc/rc.local?
Is it possible to have a conditional within /etc/rc.local?
I've checked many Q&As and most people suggest running chmod +x on it, but my problem is different. It actually does work for me without ...
0
votes
1answer
48 views
What is the difference between sending carbon copies of mail message to other users and sending mail to multiple users at the same time
In Unix, the -c option in mailx command sends copy of message to other people and has the following syntax:
mailx -s "Subject" -c "jpm,sumit" charlie < message.txt
where jpm ...
20
votes
1answer
2k views
Using mv command to move a file from one folder to another one - Strange example
I'm learning unix commands from a UNIX Tutorial for Beginners at surrey.ac.uk where I found a weird way to move a file. In particular, I have the folder unixstuff in the home directory, inside the ...
0
votes
0answers
33 views
Syntax for using systemd-run to limit CPU and memory usage of multiple processes?
I would like to use Linux control groups (cgroups) to limit CPU and RAM usage of multiple processes. If the processes are Process 1 and Process 2 with child process Process 2 Sub, would this be the ...
2
votes
1answer
186 views
How do I syntax check a Zsh script?
I can do it in bash using bash -n script.sh command.
is this possible in zsh?
-1
votes
1answer
111 views
How to search OpenStreetMap for tags? [closed]
How can I have e.g. all highway speed cameras displayed on the map, i.e. what is the URL syntax to search OpenStreetMap for certain tags?
0
votes
0answers
42 views
How can I find out what experimental syntaxes my current version of Docker supports?
When I run an experimental syntax I get the following
Error response from daemon: Dockerfile parse error line 13: Unknown flag: security
When I run with DOCKER_BUILDKIT=1 I get,
I get,
[+] Building ...
0
votes
2answers
39 views
Why are these particular semicolons necessary in this function definition and command-line?
I'm preparing for the LPIC1, exam 102. This question came my way and I absolutely blanked. I knew it when I first took the quiz, now a month and a half later it's all blurred in my head.
What does ...
19
votes
4answers
2k views
Preferred syntax for two lines long pipe [closed]
When writing a long pipe it is usually clearer to separate it in two lines.
This long command line:
ruby -run -e httpd -- -p 5000 . 2>&1 | tee >(grep -Fq 'WEBrick::HTTPServer#start' &&...
0
votes
1answer
146 views
^ syntax error in awk when called via ssh
I'm running filesystem usage command to detect /var filesystem usage beyond 80% from one host to multiple remote hosts.
My command runs fine (df -h /var | awk '$1 > 80'), but with ssh it gives me ...
0
votes
1answer
145 views
What is precisely the role of the '&' character in a bash/shell redirection? [duplicate]
So as I'm writing my own shell for school, I have to implement redirections.
I've looked at the GNU Bash manual, and a fair amount of tutorials, but I'm still having troubles understanding what ...
0
votes
1answer
24 views
what `foo=bar programname` means [duplicate]
While developing a React app, I needed to use some environment variables.
The way to do it is by using this syntax:
REACT_APP_NOT_SECRET_CODE=abcdef npm start
see reference
My first question is: ...
2
votes
1answer
35 views
Temporary display full name of argument instead of short name/abbrev
After an command, where the user should give an output location with -o, I wondered if there is an (standard) command that temporary displays the full name of the given argument, like the -o, that ...
1
vote
1answer
152 views
Problem with auto-completion on VPS
I just set up a VPS with hostinger.com. The OS is Ubuntu 18.04.
I created a user account, mike.
I quickly realised that auto-completion wasn't apparently installed so looked up how you do this.
For ...
2
votes
1answer
134 views
Consolidate several GraphicsMagick (ImageMagick) commands into one
There are many times I get single page PDFs that I want to convert to JPEGs and crop the excess whitespace off of.
Here is the current set of commands I have which accomplishes what I want:
gm ...
0
votes
1answer
160 views
bash script single quote and backslash creation
I'm trying to write a bash script for a snapshot backup with rsync to a server.
The command I want to invoke is
rsync -aPh -e ssh --rsync-path='sudo rsync' --link-dest=../last /home/username/files ...
0
votes
1answer
176 views
iptables command is not accepted in parrot OS
I created my own chain called test. I want to insert a new rule in the chain that drops all packets to an IP address at a specified port.
sudo iptables -I test -j DROP -d 130.x.y.z -dport 24
The ...
4
votes
3answers
3k views
I am getting “syntax error near unexpected token `'$#''” in a simple Bash script
I'm using Debian 10 (Buster) and am getting an error in a simple Bash script. All it does is check to see if one parameter is passed in, and if it's a file, just echo out the file:
#!/usr/bin/bash
if ...
1
vote
1answer
115 views
Why should I set the source device with < > when using pv?
I have a question out of curiosity ;-)
I find that I could accomplish cloning a disk with the command pv instead of dd too.
For that I used what I found in the internet
pv < /dev/sda1 > /dev/...
11
votes
1answer
691 views
Why can't you reverse the order of the input redirection operator for while loops?
In Bash you can move input redirection operators to the front of a command:
cat <<< "hello"
# equivalent to
<<< "hello" cat
Why are you unable to do the same for while loops?
...
-2
votes
2answers
69 views
Help with indexing a list of values
I need to track a huge log and more exactly a column. In this column I have some integer values in a rage between 103 and 17431. Example of original file
402
402
402
667
942
342
990
402
For every ...
-1
votes
2answers
72 views
Defining several variables at once (copy-paste-execute in shell)
I have a list of variables I copy-paste one by one from a file to my shell and hit Enter to execute. For example:
var1="myvar1"
var2="myvar2"
Because in practice there are more variables, instead ...
0
votes
1answer
375 views
Convert Date string in timestamp
I can't find the right syntax to convert a string date in epoch timestamp.
The script is:
date -d '2012-03-02 22:00 EDT' +%s
DATEJ=`echo -n \'2012-03-02 22:00\'`
echo $DATEJ
date -d $DATEJ EDT +%s
...
-2
votes
1answer
114 views
Is there a reason to use \+ or \- in date arguments?
I use date \+%F\-%T to show date and time in this format: 2019-08-15-21:34:58.
From man date:
%F full date; same as %Y-%m-%d
%T time; same as %H:%M:%S
I recognized no explanation for \+ or \...
27
votes
3answers
10k views
What is the meaning of [[:space:]] in bash?
I just came across a bash script. What does [[:space:]] mean in a bash script?
Why the double colon?
0
votes
2answers
257 views
Set shell variable then invoke subprocess fails
I was playing with getopts, which has a shell variable OPTERR that influences its behavior. I wanted to change the value of OPTERR and invoke getopts on the same line, to affect the behavior of ...
2
votes
1answer
182 views
What is the difference between vertical pipe and juxtaposition in JQ?
My program returns JSON into stdout and it is an object with operations field, which contains a list of operations. Each operation contains fields including id fields, for example:
{
"operations":...
11
votes
2answers
666 views
Why does a brace command group need spaces after the opening brace in POSIX Shell Grammar?
TL;DR: Why does POSIX brace group need spaces after { reserved word but subshell doesn't after reserved word (?
POSIX shell grammar defines brace group and subshell as follows
brace_group : ...
0
votes
1answer
101 views
Can anyone help me figure out what this “find” command with curly braces is saying? [duplicate]
I found some old notes where someone suggest I run the following command to set some file permissions:
find /perl/lib/ -type f -exec chmod o+r \{\} \;
Would you happen to know what the \{\} part of ...
0
votes
1answer
139 views
rsync with filter to include only certain file types for specific directory trees
my rsync command looks like this:
rsync --update -rav --filter="merge $HOME/mergefilter.txt" ~/ (remote_destination):~/
My mergefilter.txt file looks like this:
+ /directory_1/***
+ /directory_2/***...
0
votes
1answer
40 views
Evaluate command based on variable at bash [closed]
I am writing a small script that would choose random file for me from the directory and execute command with this chosen filename as a parameter.
It is about choosing random .ovpn file and run sudo ...
0
votes
1answer
21 views
Is it possible to schedule an anacron single line command execution instead of sourcing a file?
Everywhere on the internet, in articles or tutorials (in the searching of "schedule an anacron command"), I find a format such as the following:
@daily 15 rsync.daily /bin/bash /home/steven/...
0
votes
2answers
1k views
syntax error near unexpected token 'elif'
I get the error on the 7th line. Any ideas? I checked for spaces and there are none.
#!/bin/bash
if test $# -eq 0
then
echo "No arguments"
elif test $# -eq 1
echo "$1"
elif test $# -eq 2
...
0
votes
2answers
108 views
Changes to bash shell script language? [closed]
i wrote a multipart script that calls rsync a few years ago and it has always worked. After a year of no use and alot of debian apt-get updates, now the script stopped working.
Main2Network1.sh ...
-1
votes
1answer
159 views
Why would calling cd (builtin) from cd (shell function) without “command” cause an endless loop?
I once read in a Bash book by O'Reilly the following (my summary):
command and enable
cd () {
echo "Improved CD !"
# Improvement one;
command cd
# Improvement two;
# Do cool ...
