In Bash, calculating the length of a string can be achieved through various methods. This tutorial will cover the most common approaches to determine the length of a string stored in a variable.
Using Parameter Expansion
The simplest way to get the length of a string is by using parameter expansion. The ${#parameter} syntax returns the length of the string stored in the parameter variable.
myvar="some string"
echo ${#myvar} # Output: 11
To assign this length to another variable, you can use the following command:
size=${#myvar}
echo $size # Output: 11
Using wc Command
Another way to calculate the string length is by using the wc command. The -m option tells wc to count characters (which may be multi-byte), while the -c option counts bytes.
MYSTRING="abc123"
MYLENGTH=$(printf "%s" "$MYSTRING" | wc -m)
echo $MYLENGTH # Output: 7
MYLENGTH=$(printf "%s" "$MYSTRING" | wc -c)
echo $MYLENGTH # Output: 7
Note that for ASCII characters, both -m and -c options will produce the same result. However, when dealing with Unicode characters that use multiple bytes, the results may differ.
Using printf Command
The printf command can also be used to calculate the string length without relying on external commands like wc. This method is more efficient, especially for large strings or in performance-critical applications.
myvar="some string"
printf -v _ %s%n "$myvar" bytlen
echo $bytlen # Output: 11
In this example, the %n format specifier stores the number of bytes written so far into the variable bytlen.
Comparison and Performance
When it comes to performance, using printf is generally faster than relying on external commands like wc. This difference becomes more noticeable when performing a large number of string length calculations.
string="Généralité"
time for i in {1..1000};do strlens=$(echo -n "$string"|wc -mc);done;echo $strlens
# real 0m2.637s
# user 0m2.256s
# sys 0m0.906s
string="Généralité"
time for i in {1..1000};do printf -v _ %s%n "$string" bytlen;done;echo $bytlen
# real 0m0.005s
# user 0m0.005s
# sys 0m0.000s
As shown above, using printf is approximately 500 times faster than relying on wc.
Conclusion
Calculating string length in Bash can be achieved through various methods, including parameter expansion, the wc command, and the printf command. When performance matters, using printf with the %n format specifier provides the most efficient solution.