Why this works:
Output=$( tail --lines=1 $fileDiProva )
##[INFO]Output = "OK"
if [[ $Output == $OK ]]; then
echo "OK"
else
echo "No Match"
fi
and this not?
Output=$( tail --lines=1 $fileDiProva )
##[INFO]Output = "OK"
if [[ $Output -eq $OK ]]; then
echo "OK"
else
echo "No Match"
fi
What's the difference?? between == and -eq?
Thanks!
-eq is an arithmetic test.
You are comparing strings.
From help test:
Other operators:
arg1 OP arg2 Arithmetic tests. OP is one of -eq, -ne,
-lt, -le, -gt, or -ge.
When you use [[ and use -eq as the operator, the shell attempts to evaluate the LHS and RHS. The following example would explain it:
$ foo=something
+ foo=something
$ bar=other
+ bar=other
$ [[ $foo -eq $bar ]] && echo y
+ [[ something -eq other ]]
+ echo y
y
$ something=42
+ something=42
$ [[ $foo -eq $bar ]] && echo y
+ [[ something -eq other ]]
$ other=42
+ other=42
$ [[ $foo -eq $bar ]] && echo y
+ [[ something -eq other ]]
+ echo y
y
Have a look at this explanation of if.
The first one == is in the section of string compare operators and it can only compare two strings.
The second one -eq is in the last section ARG1 OP ARG2(last one) and its documentation says "ARG1" and "ARG2" are integers.
-eq, -lt, -gt is only used for arithmetic value comparison(integers).
== is used for string comparison.
Related
I had written a help menu for reference about the usage of a shell script my_script.sh
echo $'\n\n'
echo $(printf '=%.0s' {1..100})
printf ' %.0s' {1..40}
echo "Welcome"
echo $(printf '=%.0s' {1..100})
echo $'\n'
arg=$1
echo "Input : $arg"
echo
if [[ arg -eq "-h" ]] || [[ arg -eq "-H" ]] || [[ arg -eq "-help" ]] || [[ arg -eq "-Help" ]] || [[ arg -eq "--h" ]] || [[ arg -eq "--H" ]] || [[ arg -eq "--help" ]] || [[ arg -eq "--Help" ]]; then
echo "Help menu requested...."
echo $'\n\n'
echo $(printf '~%.0s' {1..100})
printf ' %.0s' {1..43}
echo "Help Menu"
echo $(printf '~%.0s' {1..100})
echo $'\n'
exit 0
else
echo "Executing a program...."
./another_script.sh
fi
When I execute `myscript.sh -h' (or any of the '-' prefixed option), it goes to the if condition, but any other argument doesn't. What am I doing wrong here? I'm new to bash scripts.
Two simple problems with your if:
-eq is for integer comparison, = or == for strings
Use $arg in your if (instead of arg).
But: I would recommend using getopts instead of string comparison. This would make the part more robust, taking care of different ordering of parameters, or when one letter parameters are combined into a single argument.
Unfortunately I do not know the exact reason why your code does not work, but I can offer you a quick fix: You can write "==" instead of "-eq" and prefix your variable "arg" with a dollar sign. Then your script should work fine.
Working example (GNU bash 4.4.19):
arg=$1
if [[ $arg == "-h" ]] || [[ $arg == "-H" ]]; then
echo "Help!"
else
echo "Stop!"
fi
the -eq operation is only used for comparing numbers.
To compare strings uses the operation =
You forgot $ sign for variables arg in Bash, should be $arg
When we use variables in Bash, we should better use double quote.
use #() for multiple strings comparison.
so the if conditions [[ arg -eq "-h" ]] should be [[ "$arg" = "-h" ]]
When comparing a variable with multiple strings, we can use [[ "$arg" = #(-h|-H|--help|--HELP|--h|--H|-help|--HELP) ]].
if [[ "$arg" = #(-h|-H|--help|--HELP|--h|--H|-help|--HELP) ]]; then
echo "Help menu requested...."
echo $'\n\n'
echo $(printf '~%.0s' {1..100})
printf ' %.0s' {1..43}
echo "Help Menu"
echo $(printf '~%.0s' {1..100})
echo $'\n'
exit 0
else
echo "Executing a program...."
./another_script.sh
fi
In addition, we can use boxes(boxes - Command line ASCII boxes unlimited!
) to generate a comment box
cat <<EOF | boxes -a c -d shell -p a5 -s 30x9
HELP MENU
bla bla
EOF
output:
########################################
# #
# #
# HELP MENU #
# #
# bla bla #
# #
# #
########################################
I want to do an if statement with three conditions that have to be satisfied at the same time. I am using Ubuntu Bash for Windows and the values $c1, $c2 and $c3 are non-integer (decimal negative numbers).
if [ (( $(echo "$c1 < 0" | bc -l) )) ] && [ (( $(echo "$c2 < 0" | bc -l) )) ] && [ (( $(echo "$c3 < 0" | bc -l) )) ];
then
>&2 echo -e " ++ Constraints OK"
else
>&2 echo -e " ++ Constraints WRONG"
fi
However, I get the following syntax error in the if line: syntax error near unexpected token `('
If I just put one condition:
if (( $(echo "$c1 < 0" | bc -l) ));
it works, but when I add the three of them as AND (&&), I get the error. Can anyone help me?
Considerably more efficient (assuming you know your values are numbers, and only need to check whether they're all negative) would be:
if [[ $c1 = -* ]] && [[ $c2 = -* ]] && [[ $c3 = -* ]]; then
>&2 echo " ++ Constraints OK"
else
>&2 echo " ++ Constraints WRONG"
fi
If you want to be more specific about the permissible formats (f/e, allowing leading spaces), a regex is another option, which similarly can be implemented more efficiently than spawning a series of subshells invoking bc:
nnum_re='^[[:space:]]*-([[:digit:]]*[.][[:digit:]]+|[[:digit:]]+)$'
if [[ $c1 =~ $nnum_re ]] && [[ $c2 =~ $nnum_re ]] && [[ $c3 =~ $nnum_re ]]; then
>&2 echo " ++ Constraints OK"
else
>&2 echo " ++ Constraints WRONG"
fi
First, pass the relational AND operators into bc to get rid of some punctuation (also only invokes bc once):
if (( $(echo "$c1 < 0 && $c2 < 0 && $c3 < 0" | bc -l) == 1 ))
then
>&2 echo -e " ++ Constraints OK"
else
>&2 echo -e " ++ Constraints WRONG"
fi
Although if it were me, I would create a shell function returning a "true" exit status if bc evaluates the result of an expression to non-zero. Then you can hide most of the ugly punctuation in one place separated from your main logic:
function bc_true() {
(( $(echo "$#" | bc -l) != 0 ))
}
And write a (IMO) cleaner shell expression:
if bc_true "$c1 < 0 && $c2 < 0 && $c3 < 0"
then
...
In the following code I want to compare the command line arguments with the parameters but I am not sure what is the current syntax to compare the arguments with parameters..i.e "==" or "-eq".
#!/bin/bash
argLength=$#
#echo "arg = $1"
if [ argLength==0 ]; then
#Running for the very first
#Get the connected device ids and save it in an array
N=0
CONNECTED_DEVICES=$(adb devices | grep -o '\b[A-Za-z0-9]\{8,\}\b'|sed -n '2,$p')
NO_OF_DEVICES=$(echo "$CONNECTED_DEVICES" | wc -l)
for CONNECTED_DEVICE in $CONNECTED_DEVICES ; do
DEVICE_IDS[$N]="$CONNECTED_DEVICE"
echo "DEVICE_IDS[$N]= $CONNECTED_DEVICE"
let "N= $N + 1"
done
for SEND_DEVICE_ID in ${DEVICE_IDS[#]} ; do
callCloneBuildInstall $SEND_DEVICE_ID
done
elif [ "$1" -eq -b ]; then
if [ $5 -eq pass ]; then
DEVICE_ID=$3
./MonkeyTests.sh -d $DEVICE_ID
else
sleep 1h
callCloneBuildInstall $SEND_DEVICE_ID
fi
elif [ "$1" -eq -m ]; then
echo "Check for CloneBuildInstall"
if [ "$5" -eq pass ]; then
DEVICE_ID=$3
callCloneBuildInstall $SEND_DEVICE_ID
else
echo "call CloneBuildInstall"
# Zip log file and save it with deviceId
callCloneBuildInstall $SEND_DEVICE_ID
fi
fi
function callCloneBuildInstall {
./CloneBuildInstall.sh -d $SEND_DEVICE_ID
}
From help test:
[...]
STRING1 = STRING2
True if the strings are equal.
[...]
arg1 OP arg2 Arithmetic tests. OP is one of -eq, -ne,
-lt, -le, -gt, or -ge.
But in any case, each part of the condition is a separate argument to [.
if [ "$arg" -eq 0 ]; then
if [ "$arg" = 0 ]; then
Why not use something like
if [ "$#" -ne 0 ]; then # number of args should not be zero
echo "USAGE: "
fi
When/how to use “==” or “-eq” operator in test?
To put it simply use == when doing lexical comparisons a.k.a string comparisons but use -eq when having numerical comparisons.
Other forms of -eq (equal) are -ne (not equal), -gt (greater than), -ge (greater than or equal), -lt (lesser than), and -le (lesser than or equal).
Some may also suggest preferring (( )).
Examples:
[[ $string == "something else" ]]
[[ $string != "something else" ]] # (negated)
[[ $num -eq 1 ]]
[[ $num -ge 2 ]]
(( $num == 1 ))
(( $num >= 1 ))
And always use [[ ]] over [ ] when you're in Bash since the former skips unnecessary expansions not related to conditional expressions like word splitting and pathname expansion.
the following example shows hot to compare numbers
I give here two different ways
one way with the ">" and "<"
and second way with "-gt" or "-lt"
both ways are work exactly
so what the differences between them ? or maybe there are not difference ?
example 1
ksh
a=1
b=2
[[ $a > $b ]] && echo ok
[[ $a < $b ]] && echo ok
ok
example 2
ksh
a=1
b=2
[[ $a -gt $b ]] && echo ok
[[ $a -lt $b ]] && echo ok
ok
In your examples there are no difference, but that is just an unfortunate choice of values for a and b.
-lt, -gt are for numeric comparison
< and > are for alphabetic comparison
$ a=12
$ b=6
$ [[ $a -lt $b ]] && echo ok
$ [[ $a < $b ]] && echo ok
ok
How to compare in shell script?
Or, why the following script prints nothing?
x=1
if[ $x = 1 ] then echo "ok" else echo "no" fi
With numbers, use -eq, -ne, ... for equals, not equals, ...
x=1
if [ $x -eq 1 ]
then
echo "ok"
else
echo "no"
fi
And for others, use == not =.
Short solution with shortcut AND and OR:
x=1
(( $x == 1 )) && echo "ok" || echo "no"
You could compare in shell in two methods
Single-bracket syntax ( if [ ] )
Double-parenthesis syntax ( if (( )))
Using Single-bracket syntax
Operators :-
-eq is equal to
-ne is not equal to
-gt is greater than
-ge is greater than or equal to
-lt is less than
-le is less than or equal to
In Your case :-
x=1
if [ $x -eq 1 ]
then
echo "ok"
else
echo "no"
fi
Double-parenthesis syntax
Double-parentheses construct is also a mechanism for allowing C-style manipulation of variables in Bash, for example, (( var++ )).
In your case :-
x=1
if (( $x == 1 )) # C like statements
then
echo "ok"
else
echo "no"
fi
It depends on the language. With bash, you can use == operator. Otherwize you may use -eq -lt -gt for equals, lowerthan, greaterthan.
$ x=1
$ if [ "$x" == "2" ]; then echo "yes"; else echo "no"; fi
no
Edit: added spaces arround == and tested with 2.