Can someone please help me to understand this bash script? I am really struggling with first block and last block specifically if and then blocks of the code.
if [[ $# -ne 2 ]] ; then
echo 'Cluster name, Azure Subscription ID required as input arguments.'
echo 'Example usage: ./create_blob_container.sh <CLUSTER_NAME> <ARM_SUBSCRIPTION_ID>'
exit 1
fi
MAX_CHAR_CLUSTER_NAME=8
CLUSTER_NAME=${1}
ARM_SUBSCRIPTION_ID=${2}
ARM_STORAGE_ACCOUNT_TFSTATE_NAME=${CLUSTER_NAME}tfstate$(echo ${ARM_SUBSCRIPTION_ID}|cut -c1-
8)
RESOURCE_GROUP_NAME=stack-tfstate-rg
CONTAINER_NAME=tfstate
LOCATION=westeurope
SKU=Standard_LRS
ENCRYPTION_SERVICES=blob
if [ ${#CLUSTER_NAME} -gt ${MAX_CHAR_CLUSTER_NAME} ]; then
echo "ERROR: Project name is too long (${#CLUSTER_NAME} chars). Maximal number of allowed
chars is ${MAX_CHAR_CLUSTER_NAME}. Exiting..."
exit 1`enter code here`
fi
Thank you
The first block means if the number of the positional parametre passed to the script is not equals to 2 then the script will execute 2 echo and exit.
if [[ $# -ne 2 ]]
Here a link that might help you.
The last block means if the length of the string stored in the variable CLUSTER_NAME which is the first position parametre is greather than MAX_CHAR_CLUSTER_NAME which is 8
if [ ${#CLUSTER_NAME} -gt ${MAX_CHAR_CLUSTER_NAME} ]; then
Another link
Related
I want to create a directory in which there is a bunch of text files using a for loop. Here is my code:
#!/bin/bash
echo "enter the nums: "
read num1 num2
for (( counter=0; counter<$num2; counter++ ))
do
if [ $num1 -lt 10 ] && [ $num2 -lt 10 ];
then
mkdir $num1 && touch $num1/$num1$num2.txt
echo "$num1""$num2" > $num1/$num1$num2.txt
else
echo "you weren't supposed to do that"
fi
done
What I want to happen if for example the user entered: "2 9"
Make a directory called 2
In it make text files called 290.txt, 291.txt, 292.txt... up till 299.txt.
Instead, what happens right now is it makes the directory and gives an error that the directory already exists. I don't know the next step, please help.
The biggest problem here is that you're doing things inside the loop that really only should be done once. Specifically, the error you're getting is because it tries to create the directory every time through the loop, but you can only create it once. Also, if the user enters too large a number, it'll print multiple error messages (e.g. if num2 is entered as 500, it'll print 500 error messages). You need to do both the error check and creating the directory once, before the loop.
A second problem is that you don't add $counter to the filename, so if the user enters "2 9", it'll create a file named 29.txt nine times.
You also have some more minor issues: in general, error messages should be printed to standard error instead of standard output (you can redirect them with >&2), and if there's an error the script should exit with a nonzero status. Also, you should (almost always) put double-quotes around variable references, to avoid weird results if the variables are blank or contain whitespace or some other things. You also don't need to touch files before writing into them (using > somefile will create the file if it doesn't exist).
With these things fixed (and some stylistic tweaks), here's what I get:
#!/bin/bash
echo "enter the nums: "
read num1 num2
if ! [ "$num1" -lt 10 ] || ! [ "$num2" -lt 10 ]; then
echo "you weren't supposed to do that" >&2 # message send to stderr
exit 1 # exit with error status
fi
mkdir "$num1" || exit $? # if mkdir fails, exit with its error status
for (( counter=0; counter<$num2; counter++ )); do
echo "${num1}${num2}" > "${num1}/${num1}${num2}${counter}.txt"
done
BTW, the ! [ "$num1" -lt 10 ] tests may look a little weird; why not just use [ "$num" -ge 10 ]? I did it that way in case $num1 and/or $num2 isn't a valid number, in which case both -lt and -ge tests would fail; using a negated test makes that an error rather than a success.
I'm not fluent in bash or anything, but it looks like mkdir $num1 is called on every loop. Find out first if the directory exists.
Here you are! change the if and for statement parent and child:
#!/bin/bash
echo "enter the nums: "
read num1 num2
if [ $num1 -lt 10 ] && [ $num2 -lt 10 ]; then
mkdir $num1
for i in $(seq 0 $num2); do
touch $num1/$num1$num2$i.txt
echo "$num1""$num2""$i" > $num1/$num1$num2$i.txt
done
else
echo "you weren't supposed to do that"
fi
This question already has answers here:
How do I find the number of arguments passed to a Bash script?
(4 answers)
Check existence of input argument in a Bash shell script
(12 answers)
Closed 7 years ago.
I need to update this bash function I use for doing things with git:
push() {
a=$1
if [ $# -eq 0 ]
then
a=$(timestamp)
fi
# ... do stuff
}
but I don't know how this line works
if [ $# -eq 0 ]
I need to check for a first argument and then I need to check for a second argument.
So there will be 2 if statements.
How can I update this and how does this line work
if [ $# -eq 0 ]
The $# part is a variable that contains the number of arguments passed to the script.
The conditional statement there checks the value of that variable using -eq and it's checking if the value is zero (as in no arguments were passed).
In order to check for two arguments, you can change (or add) that line to read like this:
if [ $# -eq 2 ]
You could create a small script to look into how $# changes when you call the function with different numbers of arguments. For instance:
[Contents of "push.sh":]
push() {
echo $#
}
echo "First call, no arguments:"
push
echo "Second call, one argument:"
push "First argument"
echo "Third call, two arguments:"
push "First argument" "And another one"
If you put this in a script and run it, you'll see something like:
-> % ./push.sh
First call, no arguments:
0
Second call, one argument:
1
Third call, two arguments:
2
This tells you that the value of $# contains the number of arguments given to the function.
The if [ $# -eq 0 ] part you can add to the script, and change the 0 to some other numbers to see what happens. Also, an internet search for "bash if" will reveal the meaning of the -eq part, and show that you could also use -lt or -gt, for instance, testing whether a number is less than or greater than another.
In the end, you'll likely want to use something like the following:
a=$1
b=$2
if [ $# -lt 1 ]
then
a=$(timestamp)
fi
if [ $# -lt 2 ]
then
b=$(second thing)
fi
I want to use a script that checks whether a list of directories exists or not and at the same time it should print some custom message that I am sending.
For example:
I have a script that validates if directory exists or not:
**check.sh**
for i in $*
if [ -d "$i" ]; then
echo Found <msg-i> directory.
else
echo <msg-i> directory not found.
Now I want to call this script like this:
./check.sh $DIR1 msg1 $Dir2 msg2 $Dir3 msg3
So if DIR1 doesn't exist then I want to display message as "msg1 directory not found", similarly for DIR2 I want to show "msg2 directory not found". Here msg1 and msg2 are something I want to pass as string. How to achieve this? I am using bash shell.
Try this:
while [ -n "$1" ]
do
dir="$1"
msg="$2"
if [ -d "$dir" ]; then
echo "$msg dir FOUND"
else
echo "$msg dir NOT FOUND"
fi
shift 2
done
shift <n> command simply shifts left positional parameters passed to the script of n positions.
For example if you call a script with:
./myscript 1 2 3 4
$1 is "1" and $2 is "2"
but if you shift 2 then $1 is "3" and $2 is "4".
In this way the loop consumes 2 parameters per cycle until $1 parameter is an empty string ( -n "$1").
while condition can be written more elegantly as:
while (( $# ))
obtaining the same result.
You can also check for the second parameter (while [ -n "$2" ]) but this changes the behavior when user provides an odd number of parameters:
in the first case last directory will be checked but you'll have a strange message because $msg il empty
il the second case you'll not have strange messages, but last directory will silently not be checked
Better test parameters at the beginning:
if (( $# % 2 ))
then
echo "Provide an even number of parameters"
exit 1
fi
Chepner Says:
The while condition can simply be (( $# )) (test if the number of positional parameters is non-zero).
Chaitanya Says:
Hi Chepner, thanks for providing alternate solution, can you please tell me how the while condition should actually look like in order to use $# , I tried different ways but it is not working for me.
Here's a quick sample:
while (( $# ))
do
dir=$1
msg=$2
shift 2
[...]
done
The while (( $# )) will be true as long as there are any command line arguments. Doing the shift twice removes arguments from the list. When no more arguments, the while loop ends.
#Zac has the correct answer.
One tip for the message: use a printf format string:
./check.sh dir1 "can't locate %s directory"
and in the script:
if [[ ! -d "$dir" ]]; then
printf "$msg" "$dir"
I am learning bash.
I would like to do a simple script that, when not arguments given, shows some message. And when I give numers as argument,s depending on the value, it does one thing or another.
I would also like to know suggestions for the best online manuals for beginners in bash
Thanks
if [[ $# -eq 0 ]] ; then
echo 'some message'
exit 0
fi
case "$1" in
1) echo 'you gave 1' ;;
*) echo 'you gave something else' ;;
esac
The Advanced Bash-Scripting Guide is pretty good. In spite of its name, it does treat the basics.
If only interested in bailing if a particular argument is missing, Parameter Substitution is great:
#!/bin/bash
# usage-message.sh
: ${1?"Usage: $0 ARGUMENT"}
# Script exits here if command-line parameter absent,
#+ with following error message.
# usage-message.sh: 1: Usage: usage-message.sh ARGUMENT
Example
if [ -z "$*" ]; then echo "No args"; fi
Result
No args
Details
-z is the unary operator for length of string is zero.
$* is all arguments.
The quotes are for safety and encapsulating multiple arguments if present.
Use man bash and search (/ key) for "unary" for more operators like this.
Old but I have reason to rework the answer now thanks to some previous confusion:
if [[ $1 == "" ]] #Where "$1" is the positional argument you want to validate
then
echo "something"
exit 0
fi
This will echo "Something" if there is no positional argument $1. It does not validate that $1 contains specific information however.
If there is not only 1 argument, then print usage and exit
if [[ $# != 1 ]] ; then
echo 'USAGE: bin/siege COOKIE'
exit 0
fi
So basically I am trying to check the arguments that are passed into the script. If it has three arguments and the third argument is a 1, then I want it to continue. I also want it to continue if it has four arguments and the third argument is not a 1.
So basically I thought that I could just do...
if ([ $# -ne 3 ] and [ "$3" -ne "2" ])
then
exit 0
fi
However it seems that Bash does not have and's to use for if's,so then I figured that I could just use nested if's, however now it's complaining still. So this is what I have currently...
if [ $# -ne 3 ]
then
if [ "$3" -ne "1" ]
then
echo "Improper number of arguments.
FORMAT make-csv-data <STUDY> <TAG> <MODE> <SELECT>
Select can be left off if you want all data (Mode=1)
"
exit 0
fi
fi
if [ $# -ne 4 ]
then
if [ "$3" -ne "2" ]
then
echo "Improper number of arguments.
FORMAT make-csv-data <STUDY> <TAG> <MODE> <SELECT>
Select can be left off if you want all data (Mode=1)
"
exit 0
fi
fi
So where am I going wrong? Can I not nest if statements in Bash? Is there a super-zen way of doing this that I'm missing altogether?
Thanks for the any help you could give me.
New Problem...
Now, for some reason or another, the code isn't working at all. There are no errors or anything, it just doesn't work. It doesn't check the number of arguments. I've run the script with no arguments at all and it just skips it like it's not even there.
Weird part is that I was sure that the code was working yesterday. Come back today, not so much. Any ideas on what the problem is? (Sorry, but I have to remove the accepted answer on this.)
if [[ $# = 3 && "$3" != "1" ]]
then
echo "Improper number of arguments.
FORMAT make-csv-data <STUDY> <TAG> <MODE> <SELECT>
Select can be omitted if all data is required (Mode=1)
"
exit 0
fi
if [[ $# > 4 ]]
then
echo "Improper number of arguments.
FORMAT make-csv-data <STUDY> <TAG> <MODE> <SELECT>
Select can be omitted if all data is required (Mode=1)
"
exit 0
fi
EDIT II:
There are a few things that the Bash shell isn't liking about this script that I'm trying to do. I'll probably end up rewriting it in another scripting language and do a few more things that I have in mind for the project. Thanks for the help in any case.
if [ $# -ne 3 -a "$3" -ne "1" ]; then
exit 0
fi
For reference
-a = and
-o = or
Or, you could just use use:
if [[ $# != 3 && "$3" != "1" ]]; then
Please see:
http://bash-hackers.org/wiki/doku.php/commands/classictest#and_and_or
and
http://bash-hackers.org/wiki/doku.php/syntax/ccmd/conditional_expression
Since you're just checking exit/return values with "if", you need to provide something, e.g. a command, that provides meaningful ones based on your tests. [ is such a command, another possibility is the [[ keyword.
The actual correct examples already were mentioned by scragar above, I don't want to just repeat them :)