You can use separate_wider_position() from the tidyr package if all your labels are the same widths.

labels<- read_tsv("labels.txt")
pos <- c(6,2,2,1,3)
names(pos) <- c("samp","id","treat","sex","line")
separate_wider_position(label, widths = pos, cols = label)

This will give you the following 5 columns which you may rearrange any way you want:

# A tibble: 11 × 5
   samp   id    treat sex   line 

   <chr>  <chr> <chr> <chr> <chr>

 1 sample 10    tr    f     100  
 2 sample 11    tr    f     100  
 3 sample 12    tr    f     100  
 4 sample 13    tr    m     104  
 5 sample 14    tr    f     104  
 6 sample 15    ct    f     104  
 7 sample 16    ct    f     120  
 8 sample 17    ct    m     120  
 9 sample 18    ct    f     120  
10 sample 19    ct    m     100  
11 sample 20    ct    f     104  

Looks like it is a fixed width file, use read.fwf:

read.fwf(file = textConnection("sample10trf100
sample11trf100
sample12trf100
sample13trm104
sample14trf104
sample15ctf104
sample16ctf120
sample17ctm120
sample18ctf120
sample19ctm100
sample20ctf104"),
widths = c(8,2,1,3),
col.names = c("sample", "treat", "sex", "line"))
#      sample treat sex line
# 1  sample10    tr   f  100
# 2  sample11    tr   f  100
# 3  sample12    tr   f  100
# 4  sample13    tr   m  104
# 5  sample14    tr   f  104
# 6  sample15    ct   f  104
# 7  sample16    ct   f  120
# 8  sample17    ct   m  120
# 9  sample18    ct   f  120
# 10 sample19    ct   m  100
# 11 sample20    ct   f  104