What is wrong with using "\t" to grep for tab-separated values?

I have a .tsv file (values separated by tabs) with four values. So each line should have only three tabs and some text around each tab like this: value value2 value3 value4 But it looks that some lines are broken (there is more than three tabs). I need to find out these lines. --- I came up with following grep pattern. grep -v "^[^\t]+\t[^\t]+\t[^\t]+\t[^\t]+$" My thinking: - first ^ matches the beggining - [^\t]+ matches more than one "no tab character" - \t matches single tab character - $ matches end And than I just put it into right order with correct number of times. That should match correct lines. So I reverted it by -v option to get the wrong lines. But with the -v option it matches any line in the file and also some random text I tried that don't have any tabs inside. **What is my mistake please?** EDIT: I am using debian and bash.