I want to create a directory with increasing numbers every time I run the script. My current solution is:
COUNTER=1
while mkdir $COUNTER; (( $? != 0 ))
do
COUNTER=$((COUNTER + 1))
done
Is separating the commands in the while condition with a ;(semicolon) the best practice?
The very purpose of while and the shell's other control statements is to run a command and examine its exit code. You can use ! to negate the exit code.
while ! mkdir "$COUNTER"
do
COUNTER=$((COUNTER + 1))
done
Notice also the quoting; see further Why is testing "$?" to see if a command succeeded or not, an anti-pattern?
As such, if you want two commands to run and only care about the exit code from the second, a semicolon is the correct separator. Often, you want both commands to succeed; then, && is the correct separator to use.
You don't need to test the exit status, just check if the directory exists already and increment. Here is one way
#!/usr/bin/env bash
counter=1
while [[ -e $counter ]]; do
((counter++))
done
if ! mkdir "$counter"; then ##: mkdir failed
echo failed ##: execute this code
fi
POSIX sh shell.
#!/usr/bin/env sh
counter=1
while [ -e "$counter" ]; do
counter=$((counter+1))
done
if ! mkdir "$counter"; then ##: If mkdir failed
echo failed ##: Execute this code
fi
The bang ! negates the exit status of mkdir.
See help test | grep '^[[:blank:]]*!'
Well if you're just going to negate the exit status of mkdir inside the while loop then you might as well use until, which is the opposite of while
counter=1
until mkdir "$COUNTER"; do
:
COUNTER=$((COUNTER + 1))
done
Related
I'm trying to write a script that will only accept exactly one argument. I'm still learning so I don't understand what's wrong with my code. I don't understand why, even though I change the number of inputs the code just exits. (Note: I'm going to use $dir for later if then statements but I haven't included it.)
#!/bin/bash
echo -n "Specify the name of the directory"
read dir
if [ $# -ne 1 ]; then
echo "Script requires one and only one argument"
exit
fi
You can use https://www.shellcheck.net/ to double check your syntax.
$# tells you how many arguments the script was called with.
Here you have two options.
Option 1: Use arguments
#!/bin/bash
if [[ $# -ne 1 ]]
then
echo "Script requires one and only one argument"
exit 1
else
echo "ok, arg1 is $1"
fi
To call the script do: ./script.bash argument
Use [[ ]] for testing conditions (http://mywiki.wooledge.org/BashFAQ/031)
exit 1: by default when a script exists with a 0 status code, it means it worked ok. Here since it is an error, specify a non-zero value.
Option 2: Do not use arguments, ask the user for a value.
Note: this version does not use arguments at all.
#!/bin/bash
read -r -p "Specify the name of the directory: " dir
if [[ ! -d "$dir" ]]
then
echo "Error, directory $dir does not exist."
exit 1
else
echo "ok, directory $dir exists."
fi
To call the script do: ./script.bash without any arguments.
You should research bash tutorials to learn how to use arguments.
On MacOS Catalina, I have a bash script with
if [[ ! -f $CR/home/files/Recovery_*.txt ]]
then
echo "File does not exists in /home/files directory. Exiting" >> $log
echo "Aborted - $CR/home/files/Recovery_*txt not exist"
exit
fi
Even though there are 2 files in the directory the script exits. If I list directory contents beforehand there are 2 files. If I change it as follows the if is skipped:
if [[ `ls -la $CR/home/files/Recovery_*.txt | wc -l` -eq 0 ]]
then
echo "No files are :"
exit
fi
I am wanting to use the if -f conditional.
Any suggestions please?
Cheers, C
If you use nullglob, a glob expression that doesn't match returns an empty string. This lets us count files in bash without spawning other processes. Create an array with the expression, then check its length.
shopt -s nullglob
files=($CR/home/files/Recovery_*.txt)
if [[ ${#files[#]} -eq 0 ]]
then
echo "No files"
exit
fi
[Edited]
The error was not the variables, but the missing shebang as the script has come across from W2K3 SFU.
The tip about shellchecker.net was awesome and I will use that from now.
Thanks.
This a small bash program that is tasked with looking through a directory and counting how many files are in the directory. It's to ignore other directories and only count the files.
Below is my bash code, which seems to fail to count the files specifically in the directory, I say this because if I remove the if statement and just increment the counter the for loop continues to iterate and prints 4 in the counter (this is including directories though). With the if statement it prints this to the console.
folder1 has files
Looking at other questions I think the expression in my if statement is right and I am getting no compilation errors for syntax or another problems.
So I just simply dumbfounded as to why it is not counting the files.
#!/bin/bash
folder=$1
if [ $1 = empty ]; then
folder=empty
counter=0
echo $folder has $counter files
exit
fi
for d in $(ls $folder); do
if [[ -f $d ]]; then
let 'counter++'
fi
done
echo $folder has $counter files
Thank you.
Your entire script could be very well simplified as below with enhancements made. Never use output of ls programmatically. It should be used only in the command-line. The -z construct allows to you assert if the parameter following it is empty or non-empty.
For looping over files, use the default glob expansion provided by the shell. Note the && is a short-hand to do a action when the left-side of the operand returned a true condition, in a way short-hand equivalent of if <condition>; then do <action>; fi
#!/usr/bin/env bash
[ -z "$1" ] && { printf 'invalid argument passed\n' >&2 ; exit 1 ; }
shopt -s nullglob
for file in "$1"/*; do
[ -f "$file" ] && ((count++))
done
printf 'folder %s had %d files\n' "$1" "$count"
I have the following bash script
aws s3 sync s3://test/ s3://test-li/
if [[ ! $? -eq 0 ]]; then
echo "Unable to copy from test bucket"
exit 1
fi
Is that the right way to run a command and check its return value?
Your code will work, but any good shell script declares what shell should interpret it. You should add a first line of your script (no spaces at the left margin)
#!/bin/bash
(Or whatever is the correct path to bash in your environment). 99% that it is /bin/bash.
Your test is a slightly baroque, there is an -ne operator that you could use, i.e.
if [[ $? -ne 0 ]] ; then
. . .
Or you can go advanced, and let if directly test the return code from you aws command, i.e.
if ! aws sync s3://test/ s3://test-li/ ; then
echo "Unable to copy from test bucket"
exit 1
fi
In this case, you need the ! to have block execute.
You could even capture any output so you can review error msgs etc with
if ! aws sync s3://test/ s3://test-li/ > /tmp/aws_launchlog.txt 2>&1 ; then
echo "Unable to copy from test bucket"
exit 1
fi
IHTH
Unlike most other languages, in shells like bash the if statement is followed by a command, the brackets are fooling you. [[ is actually a shell keyword (as is !), a development of [ which is a shell built-in, also known as the test command.
Use [[ when you wish to do pattern matching, use (( when you wish to do arithmetic comparisons.
if (( some_variable > 0 ))
then
...
fi
If you just want to test if a command worked (returned zero) then any form of brackets are superfluous.
if ! aws s3 sync s3://test/ s3://test-li/
then
# Always send error messages to stderr
echo "Unable to copy from test bucket" >&2
exit 1
fi
Having said that, there are thousands of scripts out there in the wild that do what you have done, and they still work. Unfortunately.
Your way will work. A simpler way is to put the command directly in the if:
if ! aws s3 sync s3://test/ s3://test-li/
then
echo "Unable to copy from test bucket"
exit 1
fi
bash's set -e is quite useful in these cases.
#!/bin/bash
set -e
aws s3 sync s3://test/ s3://test-li/
# if `aws` returns non-zero, the following code will not be executed
echo 'it succeeded!'
I haven't found anything to deal with this particular situation. Maybe there is a easy way that I'm overlooking instead of checking for a string to catch this scenario. When I check an input for existence of a file, if the input is ~/filecheck , this won't work. I get negative results while the file is in my home folder. Any suggestions for improvement to any part of the script I will definitely appreciate. I also have to use an input instead of a argument. Thanks for any help.
my test script
read -p "Enter: " input
echo $input
if [ -f $input ]; then
read -p "Do you REALLY want to delete this file?:" input2
if [[ $input2='y' || $input2 = 'Y' ]]
then
rm -f $input
elif [[ $input2='n' || $input2='N' ]]
then
exit
else
echo "Invaild Option"
exit
fi
else
echo Invaild Option!
exit
fi
Since you are entering input string as ~/filecheck shell doesn't expand tilde while using condition with -f in [ -f $input ]
You can use it this way but it is not recommended and potentially dangerous as arbitrary commands can be run by user:
if [[ -f $(bash -c "echo $input") ]]; then
echo "file exists"
fi
EDIT: As per the comments below to avoid risky bash -c you can use:
if [[ -f "${input/\~/$HOME}" ]]; then
echo "file exists"
fi
You can't have tilde expansion in this part of the program without using something based on eval—and you don't want to do that with user input. So, your poor-man solution will be to substitute any potential leading ~/ with the expansion of $HOME/. Here's the adaptation of your script in an arguably better style:
#!/bin/bash
read -e -p "Enter: " input
input=${input/#~\//$HOME/} # <--- this is the main idea of this answer (and it's rather poor)
echo "$input"
if [[ -f $input ]]; then
read -e -p "Do you REALLY want to delete this file? " input2
if [[ ${input2,,} = y ]]; then
rm -f -- "$input"
elif [[ ${input2,,} = n ]]; then
exit
else
echo "Invalid Option"
exit
fi
else
echo "Invalid Option!"
fi
exit
Now, out of curiosity, why are you spending time to make a wrapper around rm? you're making a clunky interface to an already existing program, without adding anything to it, only rendering it less powerful and less easy to use.
If all what you want it's to ask the user before deleting, you can use:
rm -i
This will give you appropriate error in the case file does not exist.