I was writing a little bash script and noticed an odd thing. Basically it's just when I execute this:
if [ "$#" = "spam with eggs" ]
then
echo "yay"
else
echo "nay"
fi
This gives the following error:
$ sh spam.sh spam with eggs
spam.sh: 3: [: =: unexpected operator
nay
But if I change the script to the following, it works:
f="$#"
if [ "$f" = "spam with eggs" ]
then
echo "yay"
else
echo "nay"
fi
Why doesn't it work with "$#" in the first place?
Because "$#" is very specifically rigged to preserve whitespace exactly as it was. In your example, it returns three strings, not one. You want "$*" here. (That's unusual; most people have the opposite problem.)
Related
I am trying to make a function to start, stop or restart from any directory
The code works fine without any arguments but when adding any argument I get the webserver:6: = not found error, when testing the variables everything looks like it should work
function webserver {
#echo $USERNAME
'echo $1
if [ "$1" != "" ]
then
if [ "$1" == "start"]
then
/Users/$USERNAME/start.sh
fi
if [ "$1" == "stop"]
then
/Users/$USERNAME/stop.sh
fi
if [ "$1" == "restart"]
then
/Users/$USERNAME/restart.sh
fi
else
echo "Invalid arguments! Valid arguments are : start stop restart"
fi
}
Why is this code not working?
There's a single-quote before the echo $1 command, which'll cause different trouble. Is that a typo?
The mains problem is that your comparison syntax is wrong; in a [ ] test, use a single = for string equality test, and you need spaces between each syntactic element, including before the final ].
if [ "$1" == "start"] # Bad, will give errors
if [ "$1" = "start" ] # Good, will work as expected
Also, I'd replace that series of if statements with a either a case statement, or a single if ... elif ... elif, since only one branch will ever be taken.
case "$1" in
start)
/Users/$USERNAME/start.sh ;;
stop)
/Users/$USERNAME/stop.sh ;;
restart)
/Users/$USERNAME/restart.sh ;;
*) # This is the case equivalent of "else"
echo "Invalid arguments! Valid arguments are : start stop restart" ;;
esac
like Gordon said, the syntax for zsh is wrong with only one [ ].
according to "==" logical operator and zsh version 5.7.x (installed using Homebrew)
Simple answer: a == is a logical operator only inside [[ … ]] constructs.
And it works also in ksh and bash.
When used outside a [[ … ]] construct a =cmd becomes a filename expansion operator but only in zsh
$ echo ==
zsh: = not found
I just started learning Bash scripting and i have to do a program that separate between one bit map image to two (the image is broken), I already found on the web how to write loops and statements
but i don't know why my if statement is always goes to the else.
the if is modulo by 2 thats equals to 0
here is the following code
#!/bin/sh
OUTPUT="$(hexdump -v -e '/1 "%02X\n"' merge.bmp)"
echo $OUTPUT
vars=0
count=1
touch one
touch two
for i in $OUTPUT
do
if (($vars%2==0))
then
echo "1"
else
echo "2"
fi
vars=$((vars+count))
done
in the terminal the following error is
./q3.sh: 14: ./q3.sh: 2885%2==0: not found
2
i really don't know why the if always print 2
The shebang line is wrong, it should be:
#!/bin/bash
((expression)) is a bash extension, not available in sh.
The /bin/sh version of the (()) bashism is this:
if test $(($vars % 2)) -eq 0; then
echo "1"
...
fi
Since $(()) knows about variable names, you may even drop the dollar and write
if test $((vars % 2)) -eq 0; then
echo "1"
...
fi
How would be the correct bash syntax for something like this:
if [ "$actual" == "$expected" ]; then
doNothing
else
echo "Error: actual: $actual. Expected: $expected"
fi
I am looking for something that works for all possible values of the variables "actual" and "expected". The content of the variables must not be interpreted/evaluated/expanded in any way. The script does not need to be portable (a bash only solution is ok).
You could use the simplest do-nothing statement available:
if [ "$actual" = "$expected" ]; then
:
else
echo "Error: actual: $actual. Expected: $expected"
fi
(Note: One = not two in [/test.)
But a better idea is to just invert the test and remove the need for that entirely:
if [ "$actual" != "$expected" ]; then
echo "Error: actual: $actual. Expected: $expected"
fi
Did you try:
if [ "$actual" != "$expected" ]; then
echo "Error: actual: $actual. Expected: $expected"
fi
if [[ $actual != $expected ]]
then
echo "Error: actual: $actual. Expected: $expected"
fi
Using the builtin [[ has several advantages over test / [. For one, you don't get bitten if you don't quote variables containing whitespace.
[[ ]] also offers < and > for locale-aware lexicographic sorting, regular expression matching, and =~. Check man bash.
(Note Etan's comment though on at least one dissenting opinion. I haven't yet made up my mind whether this is a disadvantage or a feature to be exploited, but it is sure surprising.)
There's also the thing with putting then on a separate line, but that's just personal preference.
This if/then statement in Unix always puts me in the else statement. I am using Bash.
name="Don"
if [ "$name" == "Don" ]; then
echo "Hi Don!"
else
echo "You are not Don. You are: $name"
fi
This is my first Unix shell script, so I'm sure it's something obvious. I've checked against the style guide and other if/then examples, but don't see anything wrong: http://www.dreamsyssoft.com/unix-shell-scripting/ifelse-tutorial.php.
If you're in a POSIX shell don't use ==. Instead use =. == is specific to Bash.
name="Don"
if [ "$name" = "Don" ]; then
echo "Hi Don!"
else
echo "You are not Don. You are: $name"
fi
I executed your script and it jus tworked as expected.
If this it the full code snipped, did you propably forget to call the bash?
I am asking this because when executing the snipped with "sh", it behaves exectly as you said as this is just partial valid for sh.
So I think you missed this:
#!/bin/bash
name="Don"
if [ "$name" == "Don" ]; then
echo "Hi Don!"
else
echo "You are not Don. You are: $name"
fi
There was only one thing wrong in your original code: the line that reads
echo "Hi Don!"
The shell is trying to interpret the special character !
Try putting this line single quotes example:
echo 'Hi Don!'
I'll get to the meat and bones:
MY_VAR=6
until [$MY_VAR = 0]
do
dir/dir_$MY_VAR.log
ps | grep "NAME_$MY_VAR.ksh"
check some things
if [results = ok]
echo "program $MY_VAR sucessful"
else
echo "program $MY_VAR failure"
MY_VAR = `expr $MY_VAR - 1`
done
Now I am getting the following errors MY_VAR not found and [6: not found, so I'm assuming a rather noobish mistake. I feel the logic is sound enough just a simple syntax error I am making somewhere by the looks of the two errors I think it could be in the declaration.
You need to have a space after [ and before ] since [ is actually a command and not a delimiter.
Here is your script re-written in Bash (or ksh):
my_var=6
until ((my_var == 0))
do
dir/dir_$my_var.log # I have no idea what this is supposed to be
ps | grep "NAME_$my_var.ksh"
# check some things
if [[ $results = ok ]]
then
echo "program $my_var successful"
else
echo "program $my_var failure"
((my_var--))
fi
done
However:
for my_var in {6..1}
do
dir/dir_$my_var.log # I have no idea what this is supposed to be
ps | grep "NAME_$my_var.ksh"
# check some things
if [[ $results = ok ]]
then
echo "program $my_var successful"
else
echo "program $my_var failure"
fi
done
Your two errors are caused by:
until [$MY_VAR = 0]
MY_VAR = $(expr $MY_VAR - 1)
[I've used $() instead of backticks because I couldn't get backticks into the code section]
The first problem is the lack of spaces around the square brackets - on both ends. The shell is looking for the command [6 (after expanding $MY_VAR), instead of [ (have a look at /usr/bin/[ - it's actually a program). You should also use -eq to do numeric comparisons. = should work ok here, but leading zeros can break a string comparison where a numeric comparison would work:
until [ "$MY_VAR" -eq 0 ]
The second problem is you have spaces in your variable assignment. When you write MY_VAR = ... the shell is looking for the command MY_VAR. Instead write it as:
MY_VAR=`expr $MY_VAR - 1`
These answers directly answer your questions, but you should study Dennis Williamson's answer for better ways to do these things.