Comparing two bash variables

Question

I am trying to write a simple Bash script that shows the difference between two variables, with the assumption that both variables contain identical parameters with different values. Look at $sam and $pish variables. They are identical, except parameter driver_mode is 1 in $sam, and 2 in $pish. To do this comparison, I store each variable into a separate array, and then compare each element one by one.

#!/bin/bash sam="driver_mode=2 firmware_path=/home/release/firmware/ onebox_zone_enabled=0x10001 ta_aggr=4 skip_fw_load=0 fw_load_mode=1 sdio_clock=40000 enable_antenna_diversity=0 coex_mode=1 obm_ant_sel_val=2 wlan_rf_power_mode=0 bt_rf_power_mode=0 zigb_rf_power_mode=0 country_code=840 bt_rf_tx_power_mode=1 bt_rf_rx_power_mode=0" pish="driver_mode=1 firmware_path=/home/release/firmware/ onebox_zone_enabled=0x10001 ta_aggr=4 skip_fw_load=0 fw_load_mode=1 sdio_clock=40000 enable_antenna_diversity=0 coex_mode=1 obm_ant_sel_val=2 wlan_rf_power_mode=0 bt_rf_power_mode=0 zigb_rf_power_mode=0 country_code=840 bt_rf_tx_power_mode=1 bt_rf_rx_power_mode=0" read -r -a array_old <<< "$sam" read -r -a array_new <<< "$pish" for index in "${!array_old[@]}"; do if [[ ${array_old[index]} -ne ${array_new[index]} ]]; then echo ${array_old[index]} 'to' ${array_new[index]} fi done

Running the above bash script gives me error:

./test: line 12: firmware_path=/home/release/firmware/: syntax error: operand expected (error token is "/home/release/firmware/")

Ruslan Osmanov · Accepted Answer · 2016-11-13 07:05:41Z

5

The -ne operator is an integer comparison operator. To compare strings use !=:

for index in "${!array_old[@]}"; do if [[ ${array_old[index]} != "${array_new[index]}" ]]; then echo ${array_old[index]} 'to' ${array_new[index]} fi done

edited Nov 13, 2016 at 7:05

answered Nov 13, 2016 at 5:38

Ruslan Osmanov

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3 Comments

ruakh Over a year ago

I'd like to +1 because of your first paragraph, but then your last one cancels it out by being wrong in the exact way that the first paragraph was right. (Namely: the reason you can write index rather than $index is that array indices are an arithmetic context, exactly like the arguments of -ne.)

janos Over a year ago

@ruakh it's fixed now ;-)

Ruslan Osmanov Over a year ago

@ruakh, indeed, as ${!array_old[@]} expands to numeric indices. I'm used to use indices in string context, and completely forgot about this feature. Thanks.

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